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Three Puzzles Inspired by Ramanujan (quantamagazine.org)
159 points by aburan28 on July 14, 2016 | hide | past | favorite | 17 comments



Mind blown: The article made me realize that you can generate one of those trippy "continued fraction" equalities any time you have x on both sides of the equation, one side by itself.

Golden ratio: x = 1 + 1/x -> keep re-plugging the right-hand side into the x on the RHS:

x = 1 + 1/(1 + 1/(1 + 1/...


Generating Functions and their applications may be of interest to you.

https://en.wikipedia.org/wiki/Generating_function

A PDF on the topic: https://www.math.upenn.edu/~wilf/gfology2.pdf

I was introduced to them in Concrete Mathematics by Graham, Knuth, and Patashnik, but then got to see their application in later statistics courses.


It occurs to me that a continued surd also works here:

  x = sqrt(1 + sqrt(1 + sqrt(1 + sqrt(1 + ...


You might also have your mind blown by this esoteric result: https://news.ycombinator.com/item?id=11976554


... actually, just mired in incomprehension.


You can generate many of them, not all of them converges though.


Isn't the golden ratio x = 1/(x-1) ?


Never mind, they both work out to the same value.


I guess it is the same equation (x-1 = 1/x)


Its great to see Ramunujan getting a fair bit of attention these days. His story is really fascinating. I can recommend:

https://www.amazon.com/Man-Who-Knew-Infinity-Ramanujan/dp/06...

This was also made into a movie a couple of months ago, I haven't seen the movie but it should be on netflix/itunes by now since I don't think it had a wide theatrical release.

http://www.imdb.com/title/tt0787524/


Netflix currently says they're getting it in August 2016 (DVD; I don't know about streaming)


The house is #204 out of 288 houses. Assuming the house itself isn't counted in either sum, which wasn't too clear by the question.

I got this by the definition of triangle numbers and solving n^2 = m(m+1)/2 for integer solutions. n is the house and m is the total of all houses. As usual, I have no idea how Ramanujan did this with cont. fractions.



Thanks for the spoiler.


Sorry about that. It isn't the full answer though.


   The sum of 1..n is n(n+1)/2. A.
   The sum of 1..N is N(N+1)/2. B.
   The sum of n..N = B-A.
   We want solutions to A = B-A. Or, 1 = B-A/A
I leave the rest as an exercise for the reader. :)


I really enjoy Quanta Magazine's artwork featured on the articles!




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