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 A135870 #2 Mar 30 2012 18:37:07
%S A135870 1,2,13,246,13554,2210436,1076561037,1570714992558,6871883750090694,
%T A135870 90179738434097457084,3550105797469080332658354,
%U A135870 419263945026939228053105930844,148543119421079567735277052592081220
%N A135870 G.f. A(x) = (1 + x*A(3x))^2.
%C A135870 Self-convolution of A135869.
%o A135870 (PARI) {a(n)=local(A=1+x+x*O(x^n));for(i=0,n,A=1+x*subst(A,x,3*x)^2);polcoeff(A^2,n)}
%Y A135870 Cf. A135868, A135869.
%K A135870 nonn
%O A135870 0,2
%A A135870 _Paul D. Hanna_, Dec 02 2007