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 A188893 #7 Mar 30 2012 17:22:57
%S A188893 2,8,20,3,10,6,25,4,0,14,8,50,5,9,21,0,43,23,6,154,11,16,26,56,12,7,
%T A188893 49,34,40,342,19,25,1634,8,115,0,33,89,15,47,54,638,9,36,117,30,99,
%U A188893 204,38,17,146,133,10,62,70,18,41,49,34,4806,105,161,329,11,439,223,28,5974,20,79
%N A188893 The index of the least triangular number greater than 1 that is also an n-gonal number, or 0 if none exists.
%t A188893 NgonIndex[n_, v_] := (-4 + n + Sqrt[16 - 8*n + n^2 - 16*v + 8*n*v])/(n - 2)/2; Table[k = 2; While[tr = k*(k+1)/2; i = NgonIndex[n, tr]; k < 20000 && ! IntegerQ[i], k++]; If[k==20000, k=0]; k, {n, 3, 50}]
%Y A188893 Cf. A188891.
%K A188893 nonn
%O A188893 3,1
%A A188893 _T. D. Noe_, Apr 13 2011