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Math Education

Golden State and the Mathematical Magic of Seventy-Three (newyorker.com) 102

Charles Bethea has written a fascinating piece on the number '73' for The New Yorker. Below are some tidbits from the story but I urge you to hit the New Yorker link and read the story in entirety there. Bethea writes: "I am aware of the Warriors's push for seventy-three wins," Ken Ono, a professor of mathematics at Emory University and the author of "The Web of Modularity: Arithmetic of the Coefficients of Modular Forms and q-series," said recently. [...] Professor Ono worked as a math consultant on a film called "The Man Who Knew Infinity," which stars Dev Patel and Jeremy Irons, and which screens this week at the Tribeca Film Festival, in New York. The movie centers on the friendship of the legendary Indian mathematician Srinivasa Ramanujan (Patel) and his Cambridge University colleague G. H. Hardy (Irons), and it depicts a famous story that Hardy once told about Ramanujan. "I remember once going to see him when he was ill at Putney," Hardy said. "I had ridden in taxicab number 1729 and remarked that the number seemed to me rather a dull one, and that I hoped it was not an unfavorable omen. "No," he replied. "It is a very interesting number; it is the smallest number expressible as the sum of two cubes in two different ways." One cubed plus twelve cubed, and nine cubed plus ten cubed. This was the first of what came to be known as "taxicab numbers." [...] So what does Professor Ono think of seventy-three? "I really like the number seventy-three," he said. "It is the sixth 'emirp.'" An emirp, he explained, is a prime number that remains prime when its digits are reversed. (Emirp, of course, is 'prime' spelled backward.)
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Golden State and the Mathematical Magic of Seventy-Three

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  • I saw this on the front page while it was still littered with broken Unicode. Thanks for actually doing some editing, but you guys missed one: oetaxicab.
  • by Anonymous Coward

    My God, it's full of stars...

  • Base 10 (Score:4, Interesting)

    by Iamthecheese ( 1264298 ) on Thursday April 14, 2016 @02:01PM (#51909793)
    What's so special about base 10? There are other primes in base 9 that are also prime when the digits are reversed. And base 8. Does it really provide any useful information?
    • And when you get down to base 2 it seems like every other number is a prime and there are quite a lot of emirps in that set. ;)
      • by narcc ( 412956 )

        Can you provide an example of a number that is prime in base 2, but not prime when converted to base 10?

        No, no you can not.

        • Bah... yeah, brain fart. I'm on painkillers for my back at the moment, so... there's that. I realized my folly while writing up an explanation of how 9 is a prime in base 2 (1001)... which, of course, is not true.
    • Re:Base 10 (Score:4, Informative)

      by mrchaotica ( 681592 ) * on Thursday April 14, 2016 @02:19PM (#51909919)

      Not to mention, at what point does a number being "interesting" stop being mathematics and start being numerology? I mean, are things like taxicab numbers and 'emirps' useful for anything?

      • Re:Base 10 (Score:5, Interesting)

        by ShanghaiBill ( 739463 ) on Thursday April 14, 2016 @02:37PM (#51910075)

        Not to mention, at what point does a number being "interesting" stop being mathematics and start being numerology?

        There are no uninteresting numbers. Proof: Assume N is the smallest uninteresting number. That property in itself makes it interesting. Therefore there can be no smallest uninteresting number, so logically uninteresting numbers cannot exist. QED.

        I mean, are things like taxicab numbers and 'emirps' useful for anything?

        There is no requirement that mathematics be useful. Many fields of math, including non-Euclidian geometry, trans-infinite set theory, etc. were developed long before there were any applications. The Greeks and Romans had no use for zero. Some mathematicians consider it a badge of honor to work on a topic that is considered purely theoretical, and therefore useless.

        • There are no uninteresting numbers. Proof: Assume N is the smallest uninteresting number. That property in itself makes it interesting. Therefore there can be no smallest uninteresting number, so logically uninteresting numbers cannot exist. QED.

          I believe that's the ontological proof that you're a total nerd.

        • Re:Base 10 (Score:4, Interesting)

          by BlackPignouf ( 1017012 ) on Thursday April 14, 2016 @04:31PM (#51911163)

          There are no uninteresting numbers. Proof: Assume N is the smallest uninteresting number. That property in itself makes it interesting. Therefore there can be no smallest uninteresting number, so logically uninteresting numbers cannot exist. QED.

          Your proof is flawed, because it cannot work recursively. What about the second smallest uninteresting number? Your argument only reduces the set of uninteresting numbers by one, and until proven otherwise, there are an infinity of uninteresting numbers.
          BTW, 12407 seems to be the smallest uninteresting number http://www.kevinhouston.net/bl... [kevinhouston.net], which, as you mentioned, makes it interesting. The next smallest uninteresting number really is uninteresting, and I don't even know which one it is :)

          • he just "proved" there isn't a first uninteresting number, so there can't possibly be a second. or a third. or so on.

            idiot.

            • I might be an idiot, but you'll have to prove it ;)
              His proof is still flawed. It looks like mathematical induction (https://en.wikipedia.org/wiki/Mathematical_induction), but it really only is the base case, and there's no inductive step.
              Let's say that 12407, 12887, 13258, 13794 are the first uninteresting numbers, because they don't have any special property, and for example don't appear in https://oeis.org/ [oeis.org].
              12407 is the first uninteresting number, so let's agree this property makes it interesting. What ab

              • by Anonymous Coward

                The proof is indeed flawed, solely for the lack of proper definiton of interesting. But it does not use induction at all, it uses that natural numbers are well-ordered.

                - Let S be the set of noninteresting numbers.
                - If S is not empty then, since N is well-ordered, there exists a minimum element x of S
                - x in interesting, so x is not in S
                Contradiction, cannot happen that x belongs to S and does not belong to S.

                Hence S is emptyset.

                • As long as we're abusing inductive proofs, might as well point out that all prime numbers are odd.

                  Step One: all prime numbers except "2" are odd numbers.
                  Step Two: that makes "2" a pretty odd prime number...

      • by Empiric ( 675968 )
        I think your username and mine now compels me to assert I am indeed useful for something, at least on a coincidental, or "co-incidental", level... depending on one's notion of what is co-incidenting.
      • Even if emirps and taxicab numbers are not useful for anything, the techniques developed in proofs of assertions about things have a habit of being useful elsewhere, and the mere pondering of such things is good exercise for mathematical reasoning, and fun for those who like maths. That fun aspect should not be underrated: if you don't enjoy maths, you will tend to limit yourself only to that which has an immediately obvious usefulness. Read up on the history of maths to see how that could be a problem.

      • I mean, are things like taxicab numbers and 'emirps' useful for anything?

        Who cares? Is the Mona Lisa useful for anything?

        • Is the Mona Lisa useful for anything?

          Is the Mona Lisa mathematics?

          • Is the Mona Lisa mathematics?

            What's that got to do with anything? Is it *useful*.

            If not, then what's with the obsession that good things must have use, but only when it comes to mathematics?

            Many mathemeticians don't do maths because it's useful in the same way many artists don't do art because it's useful. Both have their uses, but that's not why we do them.

    • by jthill ( 303417 )
      All bases are base 10 in their own eyes. Special enough for you?
  • This was the first of what came to be known as 'oetaxicab numbers.'

    A what number?

    "It is the sixth 'emirp.' An emirp, he explained, is a prime number that remains prime when its digits are reversed. (Emirp, of course, is 'prime spelled backward.)

    You've got something weird going on with your quotes there.

  • by JoeyRox ( 2711699 ) on Thursday April 14, 2016 @02:15PM (#51909903)
    Find the most tenuous connection between the number 73 and sporting events and then talk about the plot of a completely unrelated movie.
    • by Potor ( 658520 )
      I have no problems with this. I had no idea this film was in production, and now I can't wait to see it. Plus I love hoops....
  • by 140Mandak262Jamuna ( 970587 ) on Thursday April 14, 2016 @02:20PM (#51909927) Journal
    The taxi cab numbers is the simplest anecdote from Ramanujan that could be told to general audience. Rest of his stuff are so far out, it is impossible to describe to even highly educated engineers. Really sad he died so young.

    But Ramanujan was never taught the process of writing down formal proofs, he self thought everything from a handbook of mathematical identities. Rediscovering several things others had already discovered and proved. He was utterly at a loss to explain how he was able to do math. He simply said, "I look at the equation or a problem. Then Goddess Namagiri Devi writes the answer in my tongue and I recite it". (not an accurate quote, paraphrased by me)

    I wish it was Lord Oppiliappan, the family deity of his dad, not Namagiri Devi the consort of the family deity of his mom. Because Lord Oppiliappan is my family deity too. Would have gotten me some bragging rights.

    • by Mes ( 124637 )

      Interesting, but that leads me to wonder why he was sure it was Namagiri Devi and not another?

    • by Shawn Willden ( 2914343 ) on Thursday April 14, 2016 @04:08PM (#51910939)

      The taxi cab numbers is the simplest anecdote from Ramanujan that could be told to general audience.

      It's recently been discovered that there is a specific reason that Ramanujan recognized the property of 1729... and it's even more mind-boggling than the idea that Ramanujan simply saw such obscure properties in random numbers.

      As it turns out, Ramanujan was thinking about Fermat's Last Theorem and had written the two sum-of-cubes decomposition of 1729 in some of his papers, as part of an exploration of FLT "near misses", numbers that are almost, but not quite, counterexamples to FLT. What's really incredible, though, was that careful study of his papers reveal that he was in the process of developing a theory of elliptic curves... moving exactly towards the technique that Andrew Wiles used to finally prove FLT in 1994/95, some 75 years after Ramanujan's death.

      Given Ramanujan's highly intuitive approach to mathematics, what this most likely means is that Ramanujan somehow just saw the structure of elliptic curve theory and its relation to FLT. Andrew Wiles is clearly one of the most brilliant mathematicians of our day, and he was only able to make and prove this connection with years of intense work and only by building upon a mass of thoroughly developed elliptic curve theory, including the Taniyama-Shimura conjecture which was proposed 35 years after Ramanujan's death, and not observed to be related to FLT until the another 30 or so years after that.

      So when Hardy mentioned 1729 to Ramanujan and was surprised at Ramanujan's observation of the number's properties, he thought that it was just evidence that Ramanujan saw odd patterns in numbers, but it was actually evidence of vastly deeper insight into the structure of number theory.

      https://plus.maths.org/content/ramanujan

      Really sad he died so young.

      Really, really sad.

      He was utterly at a loss to explain how he was able to do math. He simply said, "I look at the equation or a problem. Then Goddess Namagiri Devi writes the answer in my tongue and I recite it".

      That's not completely true. Yes, he did say that, but he was also capable of producing proofs of a sort. He tended to skip a lot of steps that were -- to him -- too obvious to bother stating, and which everyone else had to think very hard about[*], but he could and did produce work that was understandable with appropriate background and sufficient study. It seems likely that had he lived longer and obtained more formal mathematical education that he'd have developed his ability to produce formal proofs for publication.

      Ramanujan was a simply incredible mathematical intellect. I have no doubt that if he'd lived a full life he'd have done great work to advance mathematics.

      [*] Mathematicians' definition of "obvious" is rather vague. One of my favorite math jokes is about a professor lecturing to his class and saying "It's obvious that...". A student raised his hand and said "Is that obvious? I don't see it". The professor looked at the board for a long minute then walked out of class, went to his office, scribbled furiously for 20 minutes then returned to class and said "Yes, it is obvious." He then continued his lecture without further elaboration.

      • Good joke, and interesting story.
        I'm kinda good at maths, but an old pal is a few sigmas better than me. During our (math) studies, teachers realized pretty fast that he was more talented than they were. We were jealous of him, not only because he was *that* good, but also because he could write "That's obvious" 10 times in a row during an exam, skip every question till the very last, write only a few sentences and still get the best grade.

    • "I look at the equation or a problem. Then Goddess Namagiri Devi writes the answer in my tongue and I recite it".

      I suspect that deity channelling will be appearing on job requirements for H1Bs pretty soon.

    • by Applehu Akbar ( 2968043 ) on Thursday April 14, 2016 @07:29PM (#51912297)

      "But Ramanujan was never taught the process of writing down formal proofs, he self thought everything from a handbook of mathematical identities. Rediscovering several things others had already discovered and proved. He was utterly at a loss to explain how he was able to do math. He simply said, "I look at the equation or a problem. Then Goddess Namagiri Devi writes the answer in my tongue and I recite it". (not an accurate quote, paraphrased by me)"

      The other mathematician who was self-taught in the same way was Blaise Pascal. He even invented his own terminology for conventional geometric forms because his family kept him away from formal study.

  • by bromoseltzer ( 23292 ) on Thursday April 14, 2016 @02:45PM (#51910181) Homepage Journal

    "73" is well known in the telegrapher community as the code for "Best Wishes" [wikipedia.org]. It is commonly used in ham radio to this day.

  • Time to teach Golden State some new math.
  • The article defines emirp as below:

    “It is the sixth ‘emirp.’ ” An emirp, he explained, is a prime number that remains prime when its digits are reversed.

    Here are the emirp numbers: 2, 3, 5, 7, 11, 13, 17, 31, 37, 71, 73. So it is eleventh emirp.

    • Uuh -I would guess that single digit numbers are not considered emirps since it is impossible (or pointless) to reverse a single digit # (except typographically, of course) since you end up with the same value, wheras, except for 11 (which may also not be an emirps) any 2 digit or greater number can be reversed to come up with a different value. ...The whole point of emirps being the properties of a number that has actually been reversed

      -I'm just sayin'
    • by Wraithlyn ( 133796 ) on Thursday April 14, 2016 @07:47PM (#51912381)

      The actual definition is "a prime number that results in a different prime when its decimal digits are reversed."

      So, single digits, and palindromes (like 11) don't count.

  • Added to queue. Netflix still rocks.

  • I can't believe nobody has yet mentioned this clip: https://www.youtube.com/watch?... [youtube.com]

    This is why Sheldon often wears a blue shirt with the number 73 on it.

  • I first saw that story about Rajamujan and Hardy in The Penguin Dictionary of Curious and Interesting Numbers [wikipedia.org] which gave me hours of numerical pleasure.

  • Strangely, when my advisor told me that story he said it was a house number ...

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