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 A098540 #6 Jun 13 2017 22:13:25 %S A098540 1,2,5,17,81,561,5905,98673,2715025,126550129,10211715985, %T A098540 1450856148081,367849450783633,168250359224212593, %U A098540 140078954639877776273,213886080203739816320113,602782564524824650717471633 %N A098540 Row sums of triangle A098539, which shifts left one column under the matrix square. %o A098540 (PARI) a(n)=local(A,B,C,m);A=matrix(1,1);A[1,1]=1; for(m=2,n+1,B=A^2;C=matrix(m,m);for(j=1,m, for(k=1,j, if(j<3 || k==j || k>m-1,C[j,k]=1,if(k==1,C[j,k]=B[j-1,1],C[j,k]=B[j-1,k-1])); ));A=C);sum(i=1,n+1,A[n+1,i]) %Y A098540 Cf. A098539, A098541. %K A098540 nonn %O A098540 0,2 %A A098540 _Paul D. Hanna_, Sep 13 2004