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 A125531 #6 Mar 31 2012 12:35:05
%S A125531 1,4,54,3682,1209830,1909172038,14441437270426,523308354987531254,
%T A125531 90815542491916256949262,75466682574077698691682950866,
%U A125531 300268405527350796472180876929042538
%N A125531 Number of n X n arrays with entries in 1..4 in which adjacent entries differ by 1 or less (adjacent means in x or y directions).
%C A125531 [Empirical] a(base+1,n,diff)=a(base,n,diff)+F(n,diff) for base>=2.diff.(n-1) and F(n,diff)= (n=2, A063496(diff+1)) (n=3, A068744(diff+1)) (n=4, A068745(diff+1)) (n=5, A068746(diff+1)) (n=6, A068747(diff+1))
%o A125531 (S/R) stvar $[N][N]:(0.. M-1) init $[][]:=0 asgn $[][]->{*} kill +[i in 0.. N-2](+[j in 0.. N-1](($[i][j]`-$[i+1][j]`>1)+($[i+1][j]`-$[i][j]`>1)+($[j][i]`-$[j][i+1]`>1)+($[j][i+1]`-$[j][i]`>1)))
%K A125531 nonn
%O A125531 0,2
%A A125531 _R. H. Hardin_, Dec 31 2006