This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A253881 #8 Jan 17 2015 13:55:39
%S A253881 9,10,11,13,14,15,16,17,18,19,21,22,23,24,25,29,31,33,34,37,40,41,43,
%T A253881 45,46,48,49,50,51,52,54,55,56,57,60,61,62,65,68,69,70,71,72,73,74,75,
%U A253881 77,78,79,80,81,83,84,85,86,88,91,93,95,96,97,99,103,105,106,111,113,114,115,117,119
%N A253881 Positive integers N such that rational Diophantine triple {-1/N, N, (N^2-1)/N} can be extended to a quadruple.
%C A253881 Positive integer N belongs to this sequence if and only if the elliptic curve y^2 = x^3 + (N^2+1/N^2)*x^2 + x has positive rank.
%K A253881 nonn
%O A253881 1,1
%A A253881 _Thomas Bokk_, Jan 17 2015