
Exactly What It Says on the Tin, more or less. It could be a Mook, The Tagalong Kid, The New Guy, or The Idiot of the Group, but on a random lark, you show them your math homework/accounting/hyperdimensional missile schematics. Within seconds, they know what's going on, where the problem is, what to do to fix that, and then proceeds to spell it out, astonishing the entire group. When prompted, they generally explain they grew up on a math farm or something of the like or just simply, "I'm good with numbers." Can be anything from rapidfire simple math, to supplementing baseball with trig projections, but then you're just awesome that way. Is generally a Chekhov's Gun for a plotpoint later in the episode, or can evolve into a Running Gag for the series and short hand for doing mathstuff really fast. Rather logically, the Robot Buddy and The Spock often have this ability. It's also a common ability of the Idiot Savant.
Definitely Truth in Television, as quite a few people in Real Life have this ability. Most of them are mathematicians, but not all of them. In fact, there are even competitions for mental math.
May sometimes speak with a Mouthful of Pi. See also Mad Mathematician. May result from Super Intelligence.
Examples
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Anime & Manga
 Pinoko from Black Jack, who memorized her guardian's credit card number so she could follow him anywhere he went.
 Rokuro from Deadman Wonderland. Woo, he even calls himself the human calculator.
 Sadaharu Inui, the Seigaku Genius Bruiser from The Prince of Tennis. This makes him victim of Flanderization in both fanon and canon.
 Despite his general doofiness, Yakitate!! Japan's Azuma Kazuma turns out to be nothing short of a mathematical genius when he solves a cryptographic problem in base 26 in less than a minute.
 A Certain Magical Index
 It's not made a big deal of or even really mentioned outright (in the anime, anyway), but Accelerator is Good with Numbers as one of the necessary abilities to actually use his esper ability properly. The nerf he gets is actually based on brain damage that affects his mathematics ability and requires a ten thousand person Hive Mind to correct for a mere 15 minutes at a time. It Gets Better, as GROUP's enhancements are able to extend his Esper Mode to 30 minutes, then he himself manages to reduce his battery consumption by 90 percent so he can use it for undertaking longer missions.
 It's been implied that the more powerful an Esper is, the more likely that he is Good with Numbers. Dark Matter, Railgun, and Meltdowner are all very powerful espers with immense Physics (and, you guessed it, Math) knowledge. Teleporters (except Kill Point) can calculate up to the eleventh dimension.
 Index herself, due to her incredible memory, is also a hot hand at numbers.
 This is Kenji's defining ability in Summer Wars. He's so damn good he solves 2056bit encryption in his head.
 Magical Girl Lyrical Nanoha A's
 The supplementary manga revealed that, much to the competitive Alisa's chagrin, both Nanoha and Fate are like this. Fate especially, to the point where Nanoha's sister goes to her for help on her high school math homework even though Fate's in elementary school. The same chapter also mentioned that the magic in the series requires a good bit of math, so being good with numbers is one of the reasons why they're both top mages.
 There's also Hayate, who is the only known member of the TSAB with a SS ranking. Since she didn't develop her powers like everyone else she's not as good with spell control and multitasking, and has to have Long Arch or Reinforce aim for her.
 Inverted in Nichijou. Nano, a robot girl who wishes she wasn't, apparently has trouble solving "3260 plus 260, divided by 320," even going so far as to pull out an abacus to work out the problem.
 In Code Geass, several of Lelouch's Humongous Mecha require his superior mathematical skills, including his Shinkiro's absolute defense shield and the antiFLEIJA device which required incredibly complex calculations to be input within 19 seconds of use.
 Fushimi Saruhiko is revealed to be this in the interview with Misaki on the Drama CD. He manages to solve an equation Misaki came up with (just spouting numbers, basically) in a split second.
Misaki: Alright. Here we go~ Question: What is 37 + 21  44 x 17 / 4?
Saruhiko: 59.5
Misaki: ...Eh?
Saruhiko: 59.5. But if you calculate it in proper order ^{note }multiplication and division first, then addition and subtraction it would be 129.
 Cocoa of Gochuumon wa Usagi desu ka? may be very spacey, but she is something of a mathematics savant, able to calculate large sums instantly and can count prime numbers up to the thousands.
Comic Books
 Teen Genius Amadeus Cho from The Incredible Hercules can do advanced physics in his head, complete with glowing diagrams around him. He's claimed to be good enough that he can use math to stop a charging rhino with a grape seed, and proved it when he fought the freaking Hulk.
 Superman: Red Son establishes that Lex Luthor is a supergenius scientist at STAR Labs. This isn't really surprising, but this trope comes in when he casually hands his OSS handler a formula to balance the economy. However, he says it's just the principles, and the Treasury will have to do the numbercrunching for the specifics.
Films — LiveAction
 In The Dark Knight, Lau explicitly states that he is "good with calculation" while attempting to betray the whole Gotham mafia. He intends to leave with the money they entrusted him with. Had it not been for Batman and his brutal ways, he would have been able to actually make it. Though it is quite possible that the Joker himself had been planning it all since the very beginning — he is quite the CrazyPrepared guy.
 Kazan, the autistic savant in the movie Cube.
 Wynn from the prequel Cube Zero. Depending on how you interpret the ending, he may be the same person as Kazan.
 Ben Campbell from the movie 21, but that's to be expected when he counts cards as a part time job. His Establishing Character Moment is him verbally tallying up a complicated order for a customer at a clothing store, including knocking off part of the price by applying his own employee discount towards the order, all without aid of a pen and paper or calculator. In the trailer, the math is written out on screen for the benefit of the audience, though that bit was left out in the movie itself.
 John Nash of both real life and the biographic film A Beautiful Mind. He manipulates glasses of water to alter the optic lines refracting through them to match a tie on the other side, solves complex cryptograms based on the Sierpinski Gasket in his head and revolutionizes all economic theory since Adam Smith. He's also crazy as a loon.
 At the end of the third Alternate Universe liveaction Death Note movie, L adopts a Thai kid who's good with math. It's heavily suggested the kid grows up to be Near.
 Harold Crick in Stranger Than Fiction. A routine occurrence in his life is being given math equations by his coworkers, which he solves in his head instantly.
 Good Will Hunting. Will's genius is "discovered" while he's working as a janitor at MIT. In just a few minutes, he solves an impossibly complex combinatorics problem that was left on the chalkboard after everyone went home. Prof. Lambeau had given his students the entire semester to work it out.
Literature
 Andrew Jackson "Slipstick" Libby from Robert A. Heinlein's Future History series. In his introductory short story Misfit, he replaces a spaceship navigation computer by performing all spatial calculations needed to navigate the ship in real time in his head. And his mathematical genius comes to light when he warns of a critical calculation error made in setting a small nuclear charge based on what he's learned about laying the charges just by watching the officer making the calculations. (For the younger generation who've never seen one, a "slipstick" is a nickname for a slide rule, a type of analog calculation aid common before handheld calculators got good enough to do things like logarithms.)
 Also from Heinlein, Deety Carter from The Number of the Beast is as fast a calculator as Slipstick Libby. She also has a photographic memory and an incredibly precise circadian rhythm — i.e., a clock in her head. She's a slight subversion, though, in that she says that her lightning calculator ability is pointless with computers around (except that she can see a glitch in a program much more easily than most people).
 Romeo "Mo'Steel" Gonzalez from Remnants, able to tell how many years and days he had been in stasis with just a glance at a counter showing how many minutes had passed. It totaled "fivehundred years, twelve days, and some spare change."
 Meg Murry, from A Wrinkle in Time and other books by Madeleine L'Engle.
 Wraith Squadron's Voort "Piggy" saBinring is an enhanced Gammorrean, and a math genius. During dogfights, while flying and fighting on his own, Piggy is capable of keeping track of his squadronmates and the enemy, and frequently chimes in with suggestions such as "Three, recommend you break left now" and "Nine, recommend you fire now." At the end of Solo Command, his realization about the true nature of an elite enemy squadron helps save the day.
 Otto Malpense from h.i.v.e. is the archtype of this trope; he figures out the equation that a computer is using to generate a bunch of moving lasers in his head, closes his eyes, and does the equivalent of walking in between raindrops, without getting hit. Justified, seeing as he's a geneticiallyaltered clone designed to have a brain with roughly the same processing power as a uberintelligent AI, able to think both like a human and like a machine, and interact remotely with complicated computer systems and brush aside their security networks.
 In Scott Westerfeld's Midnighters trilogy, one of the special abilities you can have if you were born at midnight (and probably the most useful) is the ability to do lengthy, complex mathematical calculations easily in your head.
 Mark McHenry from Star Trek: New Frontier is specifically good with warp calculations, headings, speeds, and anything else related to navigation and piloting, much like the Star Trek examples below. In fact, at one point, a character specifically compares him to Data, in the "OK, the last time someone was this good, he was an android; what's up with this one?" sense. We eventually learn that Mark is a descendent of Apollo (from the original series), and linked at some basic level to the universe at large.
 Discworld
 The Bursar of Unseen University is this. Years ago, he was "a man whose idea of an exciting time had once been a boiled egg", and he has been driven totally, completely insane over the course of several books by Archchancellor Ridcully's habit of shouting at him and generally being as Hammy as possible. However, if you ask the Bursar a question that has anything to do with math (as his title suggests) he is able to answer it no matter which reality curve his mind is riding at the time. Since it's difficult to tell if he's really all right after things like nasty shocks, in later books this becomes a way of diagnosing him; if he can still answer a math question correctly and immediately, he's perfectly fine. Ridcully even seems to know this:
Chair of Indefinite Studies: I don't see why. Just because he can do things with numbers doesn't mean everything else is fine. Ridcully: Doesn't need to be. Numbers is what he has to do. The poor chap might be slightly yoyo, but I've been reading about it. He's one of these idiot servants. Dean: Savants. The word is savants, Ridcully. Ridcully: Whatever. Those chaps who can tell you what day of the week the first of Grune was a hundred years ago — Bursar: — Tuesday — Ridcully: — but can't tie their boot laces.
 By Unseen Academicals, however, he has either lost several more of his faculties or just been retconned into an incompetent — Unseen University's finances are in a mess and Ponder Stibbons has had to take on the Bursar's job (in addition to his twelve official positions, and probably just about everything else that needs to get done, ever) because he "regards the decimal point as a nuisance". An Alternate Character Interpretation of this is that after discovering imaginary numbers and ndimensional manifolds in The Science of Discworld, he refuses to descend from higher maths back to boring old arithmetic, and is trying to do the accounts with alephnull and "umpt".
 Granny Weatherwax is described in Maskerade as "grudgingly literate, but keenly numerate". It takes her seconds to deduce how much Nanny Ogg is being screwed by the publisher of her cookbook, even taking into consideration things like the cost of materials and distribution. She is also able to figure out the finances of the opera house, which were expertly tampered with and deliberately obfuscated to hide an embezzlement scam.
 Pyramids introduces the greatest mathematician on the Disc... "You Bastard", a camel. Apparently, Discworld camels are secretly alarmingly intelligent and spend most of their time doing extremely complex equations in their heads. Although if they are bothered enough by some puny human, they can revert to good old trajectory calculation for a wad of spit in a heartbeat.
 Mr. Bent in Making Money is exceedingly good with numbers, so much so that it's a momentous bankclosing event when he makes a mistake. He also finds the imprecision of the Bank clocks "offensive" and fixes them several times a day. By the end of the book we find out that he was raised by a caravan of traveling accountants after running from the circus.
 Talen from The Elenium is of the "can do normal math really fast" variety, which he claims developed from practice, and the need for a thief to do onthespot appraisals and fence stolen goods. His skill instead comes into play during the Church election's political maneuvering and vote tallying.
 The atevi from C. J. Cherryh's Foreigner series. Forming grammatically correct sentences in their language requires mentally doing simple algebra, and they all have the ability to instantly and accurately count things. Further, their cultures have developed a number of extremely complex systems of numerology, which the majority of atevi treat as Serious Business.
 Opal from The Vampire Files used to earn extra tips as a waitress by solving math problems in her head as a bar trick. When she did this for a mob boss, he hired her on the spot as a bookkeeper: a job at which she excelled so well that she figured out how much he'd been skimming off the top, based on indirect evidence in his gang's finances.
 Keladry, the protagonist of Protector of the Small, is very good at math. During her page years it's her best subject, and it allows her to assist in engineering projects when she becomes a knight commanding a fort.
 Thursday's daughter Tuesday in the Thursday Next books is possibly the greatest mathematical genius of all time. She proved there are seven more even numbers than odd ones, and her boyfriend Gavin discovered a three digit even prime number. Not bad going for a sixteen year old.
 The title character of Horatio Hornblower does math effortlessly and finds it hard to understand how other people have difficulty. This makes him very good at navigation and whist.
 The mice from The Underland Chronicles, judging by their Theme Naming, and Lizzie in Gregor and The Code of Claw.
LiveAction TV
 Lulu from True Jackson VP. In one episode, she's hired to be an assistant. When she finishes all the work, another coworker asks her to solve a math problem on the chalkboard. After a while, she figures out the board was upside down and turns it the right way and solves it.
 River Tam from Firefly:
Kaylee: She just did the math. Zoe: You understand how that sounds? Jayne: What? She killed them with math. What else could it have been?
 Face, on The ATeam, is brilliant with numbers. Naturally he's in charge of the team's finances, which he keeps record of in a little black book (not that he needs it — he's really good at mental math).
 Malcolm from Malcolm in the Middle can do mental math with Credit Cards Numbers. At one point he helped his dad win at poker by being able to calculate the exact probabilities of the availability of certain cards.
 Doctor Who
 In the serial "The Invasion", Zoe calculates the trajectories to destroy the Cybermen's entire invasion fleet with a handful of missiles. In her head. In thirty seconds. It works a treat.
 Adric is the proud possessor of a badge for mathematical excellence, and has demonstrated proficiency at the realitywarping mathematics that is Block Transfer Computation.
 The Doctor himself is often described as a genius and occasionally demonstrates. In the Expanded Universe novel Interference, the Doctor briefly transports himself out of a cell using pure mathematics (presumably the same Block Transfer Computation that Adric used).
 In the revival (and as a more Hidden Depths example), Donna Noble puts the number skills she requires as an office temp to work in the episode "The Doctor's Daughter".
 In the episode "42" the Doctor effortlessly solves a mathematical riddle by recognising a series of Happy Primes.
The Doctor: Honestly, don't they teach recreational mathematics anymore.
 In "The Impossible Planet" the Doctor works out the gravitational mathematics of a gravity cone extending from a black hole with a pocket calculator in a matter of minutes.
Captain: It took us two years to work that out!
The Doctor: (Shrugs) I'm very good.
 Sayid establishes his "good with numbers" cred in the pilot of LOST by figuring out that 17,294,535 iterations of a 30second message would take 16 years, 5 months. It takes him about one cycle of the message to calculate this.
 Professor Charlie Eppes from NUMB3RS, who uses his skills to solve homicides.
 On Friends Chandler is irked whenever people concede that "numbers" is about all he has going for him. "Math? You're giving me math?"
 On Star Trek: Deep Space Nine, Dr. Bashir starts displaying this characteristic after it's revealed that he's genetically engineered and therefore has (among other benefits) a superior brain.
O'Brien: The core matrix is fried. We don't have warp drive. Garak: Forgive my ignorance, but if we don't have warp drive, how long is it going to take us to reach the closest Federation starbase? O'Brien: A long time, Mr. Garak. Garak: How long? Bashir: Seventeen years, two months and three days, give or take an hour.
 Star Trek: The Next Generation: Likewise, Data is pretty good at math.
 Lisa from NewsRadio often does large calculations in her head. People tend to ask her large multiplication questions whenever they can fit it into a conversation.
 James May on Top Gear, at least by comparison to his somewhat Book Dumb copresenters.
 Eli Wallace from Stargate Universe is a math prodigy. He is recruited into the Stargate program after solving a mathematical proof embedded in a video game. His math skills periodically come in handy, such as in "Light" when he quickly works out an intercept course for the shuttle.
Rush: Whoawhoawhoa. Eli, there's many variables here. Are you sure about this? Eli: Math boy.
 Put it this way: Rush is an Insufferable Genius of the highest caliber, who can barely tolerate working with others because they can't keep up with his thought processes. He admits that Eli is smarter than him in some respects, and if he ever admits he needs help with something, Eli's the guy he goes to for it.
 Near the end of The Prisoner, Number Six mentions being good with figures, though it's not prominently demonstrated — it's probably more for ironic contrast with his resistance to being numbered.
 The pilot episode of White Collar demonstrates Caffrey's amazing mathematics. He calculates 64 years of compound interest in a few seconds, then follows that up with the much more difficult task of dividing 600 by 4.
 Matt, Shirley's Love Interest in The Adventures Of Shirley Holmes. He even goes to a school for genius kids, and helps Bo with the answers in a mathbased Game Show so he'll be able to get in as well.
Bo: Some geniuses! They can't even count. Matt: They're calculating pi. Bo: Oh.
 Fred Burkle from Angel is a math genius, and often uses the skill to help the team. Her math skill is so great that, in one episode, a group of demons attempts to cut off her head and steal her brain after she solves a puzzle for them.
 Adam Savage of the MythBusters has been shown occasionally counting how many frames of highspeed camera footage an object takes to cross a given distance (typically a foot), then doing a series of rapidfire mental calculations in order to find out its speed in miles per hour.
 In earlier seasons, he'd give the chance of something happening in percentages. Every time, he got it to add up to 100%. (Even Jamie managed to fall victim to Too Many Halves at least once.) After the fact, he did occasionally forget the actual ratios he'd used, though.
 Olivia Dunham on Fringe is shown to have an eidetic memory for numbers and patterns, but it apparently doesn't grant her any greater ability to perform calculations.
 In Spartacus: Blood and Sand, the gladiator Ashur uses this talent to gamble, and when he becomes crippled, his master allows him to be his accountant.
 In Kaamelott, Perceval is an Idiot Savant. He is utterly clueless about mapreading and cardinal points, can't go in a forest without getting lost, don't understand a thing about dates and fail even the most basic logic... Yet he is a goddamn genius with numbers and mathematics; he can do mental calculations lightningfast, understands games with impossibly complicated rules, and is apparently unbeatable at the shell game....
 Nash Bridges had Barry Chen in "Wild Card." He was played by Tommy Chong, but as Nash points out about Barry, the Comptroller for the Chinese Triads in San Francisco, that if he gets involved with anything with numbers, he goes from "idiot" to "savant" very quickly. Played for Drama since Barry had cleaned out Cedrick "Rick" Hawks at poker, and Barry told Rick, "Those hands were golden" when Rick thought Barry cheated.
 In a classic Saturday Night Live sketch, Phil Hartman plays Ronald Reagan as a friendly, slightly dim old man for the cameras and the public, but a genius mastermind behind closed doors, including the ability to do complex calculations in his head.
President Reagan: Bye bye! (Girl Scout exits Oval Office) Okay, back to work! (staff reenters) Afghanistan needs more money. We've got $65.2 million tucked away in Zurich. Now, if we hold it there for another 30 days, at 7.28% interest, that's.. roughly.. $400,000. Staffer #1: (with calculator) $397,200.. President Reagan: .. and 85 cents! I know! Don't waste my time! But.. if we take out only $20 million, we lose.. let's see, let's see.. that's.. Staffer #1: $121,800.. President Reagan: and 16 cents! Thank you so much!
Tabletop Games
 GURPS has the advantage Lightning Calculator to simulate this; the second level of it allows the character to do things like highlevel engineering design in their head instantly.
 The Talent "Lightning Calculator" in Hero System lets a character do things like calculate an approach orbit for his spaceship in twelve seconds. Simpler calculations such as multiplying 4824 by 5933 would only take one second.
Video Games
 The World Ends with You
 Sho Minamimoto, to the point of almost having the whole trope named after him. It even carries into his stats. His Hit Points are 3141 when you fight him at the end of Week 2, and his Taboo Form Hit Points are 5926. Put them together and tuck a decimal point behind the three and you have the first eight digits of pi.
 Neku could also apply for being able to belt out the square root of 3 at the drop of a hat (during day two of the second week, for those who wanted to know), but he could also have a calculator on his phone.
 Joshua is good enough with numbers to at least keep up with Minamimoto's ranting, though his status as the Composer might have something to do with this.
 Dmitri Petrovich of Backyard Sports has this, coupled with the ability to use mnemonics to remember stats.
 Ran Yakumo of the Touhou series. She once calculated the width of the Sanzu River out of boredom. Note that the Sanzu River is the mystical river of the dead and that its width constantly changes whenever someone passes through it. In Curiosities of Lotus Asia, when Rinnosuke first saw a computer and learned that it's used for, he interpreted them as being the outside world's version of familiars like Ran, because they're slaves that are used to calculate things quickly. Of course, since a familiar's power is derived from its master, Yukari Yakumo is even better at numbers than Ran, and Ran mentions that if Yukari wanted, she could have calculated the depth of the Sanzu River as well, even though it's known to be bottomless.
 N from Pokémon Black and White. He rambles about forumlas several times, and is seeking "the equation to change the world".
 Trevor from Grand Theft Auto V is. He knows exactly how much cargo comes through the port of Los Santos every year and exactly how much it's worth, and in the "Subtle" approach for the final heist, mentally calculates how much the four tons of gold they're carrying is worth when told the individual value of each bar faster than the bank manager can. Wade even states plainly that Trevor is really good with numbers.
Web Animation
 Red vs. Blue subverts this with Simmons proclaiming to be able to multiply large numbers in his head instantly. He can't.
Grif: What's... 32 times 56? Simmons: 31,452. Sarge: Is that right? Simmons: Yes. Sarge: That's pretty impressive! Simmons: I know. It's a gift.
 The correct answer is 1792. God knows where he got 31,452. Even 100 times 100 is only 10,000.
Web Comics
 Laetre, a hamster showed some mathematical aptitude in one comic of Hamleto the Hamster.
 Dubious Company: This is the closest Future High Priestess Sal gets to superpowers, since religion is NOT magic. She can rapidly calculate the probability of anything based on known factors. Heartwrenching when she calculates the odds of escaping Kreedor's castle before her execution as 0%.
 The Order of the Stick: Kobold Chancellor Kilkil shows on several occasions that he's Good with Numbers. No surprise here, as he's the main accountant of a whole Lawful Evil Empire.
 Parson Gotti of Erfworld isn't innately good with numbers. But he does have a pocket calculator, which in the game is regarded as something of a magic artifact, and is insanely good at calculating battle outcome probabilities (this is only partially due to the calculator). At least everything thinks he is. Probabilities being what they are, it's hard to prove one way or the other.
Web Original
 Andi, the protagonist of Lovelace One Two, goes from being a poor maths student to spontaneously able to solve problems as fast as she can speak or write at the beginning of the story.
 The Number Man of Worm, who has this as an actual superpower, to the point where he can calculate the exact probability of any outcome in the middle of combat, and in his youth was a legendary, undefeated member of the Slaughterhouse Nine. His power's broad scope also enables him to trivially crack encryption, model statistics on a large scale, and play the world economy like a fiddle.
Western Animation
Real Life
 Taken Up to Eleven in by Scott Flansburg as seen in Stan Lee's Superhumans. He can do extremely complex math faster than a human using a real calculator.
 Carol Vorderman originally got the job on Countdown in part due to her ability to solve the Numbers Round in her head.
 Her Australian counterpart Lily Serna is equally adept. Some of her solutions beggar belief.
 Kim Peek, the real life inspiration for Rain man.
 Arthur Benjamin is a Mathemagician, combining magic tricks with phenomenal mathematical ability. In his TED talk he squared a five digit number in his head correctly in just a couple of minutes, prompting a standing ovation.

