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 A125804 #5 Jun 14 2017 00:16:12 %S A125804 1,2,12,238,15200,3013980,1828979530,3373190565626,18837339867421686, %T A125804 317817051628161116674,16176220447967300610844988, %U A125804 2481251352301850541661479580329,1146112129196402690505198891390847384 %N A125804 Main diagonal of table A125800. %C A125804 Table A125800 is related to partitions into powers of 3; column k of A125800 equals row sums of matrix power A078122^k, where triangle A078122 shifts left one column under matrix cube. %o A125804 (PARI) a(n)=local(q=3,A=Mat(1), B); for(m=1, n+1, B=matrix(m, m); for(i=1, m, for(j=1, i, if(j==i || j==1, B[i, j]=1, B[i, j]=(A^q)[i-1, j-1]); )); A=B); return(sum(c=0,n,(A^n)[n+1,c+1])) %Y A125804 Cf. A125800, A078122; columns: A078125, A078124, A125801, A125802, A125803; A125805 (antidiagonal sums). %K A125804 nonn %O A125804 0,2 %A A125804 _Paul D. Hanna_, Dec 10 2006