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 A129102 #5 Jun 14 2017 00:27:55 %S A129102 1,4,20,136,1360,21204,537748,22891448,1675538928,214841466180, %T A129102 48966357498452,20069542925092392,14932742187505262032, %U A129102 20328765555338724571508,50972424276515393704138196 %N A129102 Column 2 of triangle A129100; also equals column 0 of matrix power A129100^4. %o A129102 (PARI) a(n)=local(A=Mat(1),B);for(m=1,n+3,B=matrix(m,m);for(r=1,m,for(c=1,r, if(r==c || r==1 || r==2,B[r,c]=1,if(c==1,B[r,1]=sum(i=1,r-1,A[r-1,i]), B[r,c]=(A^(2^(c-1)))[r-c+1,1])); )); A=B); return(A[n+3,3]) %Y A129102 Cf. A129100 (triangle); A129092 (column 0), A129101 (column 1), A129103 (column 3). %K A129102 nonn %O A129102 0,2 %A A129102 _Paul D. Hanna_, Mar 29 2007