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 A113356 #5 Jun 13 2017 22:51:27 %S A113356 1,4,18,112,965,10957,156699,2727793,56306695,1350043964,36979531548, %T A113356 1141573025171,39272377323692,1491452150268435,62027842189908230, %U A113356 2805631215820328991,137199563717151509076,7215932308408758314446 %N A113356 Column 0 of triangle A113355, which is the matrix square of A113350. %F A113356 a(n) = A113346(n+1) - 1, where A113346 equals column 0 of triangle A113345 (=A113340^2). %o A113356 (PARI) a(n)=local(A,B);A=matrix(1,1);A[1,1]=1;for(m=2,n+1,B=matrix(m,m); for(i=1,m, for(j=1,i,if(i<3 || j==i || j>m-1,B[i,j]=1,if(j==1, B[i,1]=1,B[i,j]=(A^(2*j-1))[i-j+1,1]));));A=B); (matrix(#A,#A,r,c,if(r>=c,(A^(2*c))[r-c+1,1]))^2)[n+1,1] %Y A113356 Cf. A113340, A113350, A113355, A113357 (column 1), A113358 (column 2), A113359 (column 3). %K A113356 nonn %O A113356 0,2 %A A113356 _Paul D. Hanna_, Nov 08 2005