%I #8 Mar 31 2012 12:35:02
%S 1,18,214,2202,25862,310258,3787948,46645456,577150510,7159272162,
%T 88927443434,1105386497794,13745406254372,170957599435056,
%U 2126500579257954,26452521788330842,329064936891773982
%N Number of base 18 circular n-digit numbers with adjacent digits differing by 7 or less.
%C [Empirical] a(base,n)=a(base-1,n)+F(7) for base>=7.int(n/2)+1 and F(d) is the largest coefficient in (1+x+...+x^(2d))^n
%o (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-1](($[i]`-$[(i+1)mod N]`>7)+($[(i+1)mod N]`-$[i]`>7))
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006