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 A126502 #11 Jun 01 2017 12:06:20
%S A126502 1,7,43,269,1679,10483,65449,408623,2551187,15928021,99444631,
%T A126502 620870267,3876326801,24201367447,151098247483,943363239389,
%U A126502 5889771828959,36772062710083,229581830200249,1433365791134783
%N A126502 Number of base 7 n-digit numbers with adjacent digits differing by four or less.
%C A126502 [Empirical] a(base,n)=a(base-1,n)+9^(n-1) for base>=4n-3; a(base,n)=a(base-1,n)+9^(n-1)-2 when base=4n-4.
%F A126502 Conjectures from _Colin Barker_, Jun 01 2017: (Start)
%F A126502 G.f.: (1 + x - x^2) / (1 - 6*x - 2*x^2 + 3*x^3).
%F A126502 a(n) = 6*a(n-1) + 2*a(n-2) - 3*a(n-3) for n>2.
%F A126502 (End)
%o A126502 (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-2](($[i]`-$[i+1]`>4)+($[i+1]`-$[i]`>4))
%Y A126502 Cf. Base 7 differing by three or less A126475, two or less A126394, one or less A126361.
%K A126502 nonn,base
%O A126502 0,2
%A A126502 _R. H. Hardin_, Dec 28 2006