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 A135883 #2 Mar 30 2012 18:37:07
%S A135883 1,3,15,99,814,8057,93627,1252752,19003467,322722064,6071897378,
%T A135883 125464556309,2826120900315,68954181763586,1812280504183309,
%U A135883 51059994255961903,1535575877864707548,49107734497585814006
%N A135883 Column 2 of triangle A135880.
%e A135883 Equals column 2 of triangle P=A135880:
%e A135883 1;
%e A135883 1, 1;
%e A135883 2, 2, 1;
%e A135883 6, 7, 3, 1;
%e A135883 25, 34, 15, 4, 1;
%e A135883 138, 215, 99, 26, 5, 1;
%e A135883 970, 1698, 814, 216, 40, 6, 1;
%e A135883 8390, 16220, 8057, 2171, 400, 57, 7, 1; ...
%e A135883 where column k of P^2 equals column 0 of P^(2k+2)
%e A135883 such that column 0 of P^2 equals column 0 of P shift left.
%o A135883 (PARI) {a(n)=local(P=Mat(1),R,PShR);if(n==0,1,for(i=0,n+1, PShR=matrix(#P,#P, r,c, if(r>=c,if(r==c,1,if(c==1,0,P[r-1,c-1]))));R=P*PShR; R=matrix(#P+1, #P+1, r,c, if(r>=c, if(r<#P+1,R[r,c], if(c==1,(P^2)[ #P,1],(P^(2*c-1))[r-c+1,1])))); P=matrix(#R, #R, r,c, if(r>=c, if(r<#R,P[r,c], (R^c)[r-c+1,1]))));P[n+3,3])}
%Y A135883 Cf. A135880; other columns: A135881, A135882, A135884.
%K A135883 nonn
%O A135883 0,2
%A A135883 _Paul D. Hanna_, Dec 15 2007