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 A239971 #8 Apr 01 2014 10:25:33 %S A239971 8,4,10,16,22,6,34,40,14,52,58,8,16,76,82,24,94,100,106,10,23,124,20, %T A239971 136,142,25,36,160,22,12,178,184,55,46,202,208,54,220,226,34,56,14,26, %U A239971 31,262,36,274,66,49,89,28,304,65,316,76,16,48,84,346,352,358,86,50,376 %N A239971 Least k>1 such that triangular(n) + triangular(n+k) is a square. %C A239971 For n>0, a(n) <= 6*n-2 because triangular(n) + triangular(7*n-2) = (5*n-1)^2. %o A239971 (PARI) triangular(n) = n*(n+1)/2; %o A239971 s=[]; for(n=0, 100, k=2; while(!issquare(triangular(n)+triangular(n+k)), k++); s=concat(s, k)); s \\ _Colin Barker_, Mar 31 2014 %Y A239971 Cf. A000217, A232177. %K A239971 nonn %O A239971 0,1 %A A239971 _Alex Ratushnyak_, Mar 30 2014