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 A069695 #4 Dec 05 2013 19:55:17
%S A069695 0,1,3,6,10,15,21,28,36,45,55,66,78,91,136,231,435,630,333336
%N A069695 Triangular numbers with internal digits 3.
%C A069695 For proof of finiteness see A069693.
%t A069695 Do[ If[ Union[ Drop[ RotateLeft[ IntegerDigits[n(n + 1)/2]], -2]] == {3}, Print[n(n + 1)/2]], {n, 14, 2 10^6}]
%Y A069695 Cf. A069675 to A069684, A069693 to A069700.
%K A069695 fini,full,nonn,base
%O A069695 1,3
%A A069695 _Amarnath Murthy_, Apr 06 2002
%E A069695 Extended by _Robert G. Wilson v_, Apr 07 2002