Quote:
Originally Posted by fivemack
To find Machinlike formulae for pi, I want to find sets of N where N^2+1 has only small prime factors. Tangentially, it would be nice to have a proof that, for example, n=485298 is the largest number where n^2+1 has no prime factor greater than 53.

See:
http://oeis.org/A185389 (somewhere there could be a longer computed list also).
This problem is solvable by
https://en.wikipedia.org/wiki/St%C3%B8rmer%27s_theorem using a Pell type equation, where on the right side there is a 1 not 1.