Arthur Benjamin, The Mathemagician Or Man Calculator

by mindhacker on November 9, 2009

Dr. Arthur Benjamin is a math professor at Harvey Mudd College with a Phd in Mathematical Sciences from John Hopkins University and that’s the only normal thing about this genius. According to his home page he is the author of 3 books including the very engaging “Proofs That ReallyCount”, a candid introduction to the field of  combinatorics. But that’s all still normal. His real prowess lies in doing mind math. He can square five digits numbers faster than I can type them in a  calculator. He calls himself a Mathemagician and according to his CV has a hobby of “racing calculators and performing magic”. Here is a video of a lecture or rather a performance he gave,

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One hell of a math nerd if there ever was one and he relishes his almost magical skill. Also I was going through his research papers and he sure does a good job at giving a bigger picture of what he’s trying to explain and how everything fits together to make a whole. Here is a shorter version of the above video.

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  • Not sure how he would handle the 20% likely situation where the result could be 0 or 9 - maybe there's another level to this I haven't appreciated yet.
  • For this to work, he needs one of the random two-digit numbers that he gets given to square to be divisible by three - roughly 80% likely given four random numbers, and if it didn't happen, he'd either drop the trick or come up with another way to get the number he wanted.
  • The rest is just crazy, though. I can get my head around memorizing all two-digit squares, and may even be able to do it with practice, but the four-and five-digit stuff blew me away.
  • I figured out the "tell me six digits and I'll tell you the seventh" trick.For this to work, he needs one of the random two-digit numbers that he gets given to square to be divisible by three - roughly 80% likely given four random numbers, and if it didn't happen, he'd either drop the trick or come up with another way to get the number he wanted.
  • Just crazy, though,I can get my head around memorizing all two-digit squares, and may even be able to do it with practice, but the four-and five-digit stuff blew me away.
  • this guys are amazing
  • This guy is simply amazing. I think they probably have and he's also written a book about mind math, so I guess he'll be open to the idea.
  • Amazing dude..that's great..i just can't believe it.I can get my head around memorizing all two-digit squares, and may even be able to do it with practice, but the four-and five-digit stuff blew me away.
  • I'm chuffed that I figured out the "tell me six digits and I'll tell you the seventh" trick. For this to work, he needs one of the random two-digit numbers that he gets given to square to be divisible by three - roughly 80% likely given four random numbers, and if it didn't happen, he'd either drop the trick or come up with another way to get the number he wanted. That would make the square divisible by nine, and he simply uses the "sum of digits is also divisible by nine" trick. Not sure how he would handle the 20% likely situation where the result could be 0 or 9 - maybe there's another level to this I haven't appreciated yet.

    The rest is just crazy, though. I can get my head around memorizing all two-digit squares, and may even be able to do it with practice, but the four-and five-digit stuff blew me away.
  • Awesome! This guy is simply amazing.
  • This is old as dirt guys..
  • nanoloupe
    I was wondering just the other day if anyone was doing fMRI on any of these guys with built-in lightning calculators. Does anybody know him well enough to ask if his skill has been studied with functional neurological scans? Is it raw speed in standard patterns, or does he use unusual neural pathways possibly augmented by increased signal patterns more often associated with memory?
  • I think they probably have and he's also written a book about mind math, so I guess he'll be open to the idea.
  • mk
    Holy crap..that is insane!
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