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.
1; 2,1; 1,5,6; 22,21,13,1; ...
A107783 := proc(n,k) option remember ; if n < 0 or k < 0 or k > n then 0 ; elif n =0 then 1; elif n mod 2 = 1 then if n = k then 1; else A107783(n,k+1)+A107783(n-1,k-1)+A107783(n-1,k)+A107783(n-2,k-1) ; fi ; else if k = 0 then 1; else A107783(n,k-1)+A107783(n-1,k-1)+A107783(n-1,k)+A107783(n-2,k-1) ; fi ; fi ; end: for n from 0 to 11 do if ( n mod 2 ) = 1 then kstrt := n ; else kstrt := 0 ; fi ; kend := n-kstrt : for k from kstrt to kend by sign(kend-kstrt) do printf("%d,",A107783(n,k)) ; od: od: # R. J. Mathar, Aug 13 2007