%I #8 Mar 31 2012 12:35:02
%S 1,18,168,1308,11788,108368,1019238,9713414,93465716,905458656,
%T 8814132218,86094716902,842995538722,8268296567458,81194927188214,
%U 798010003387898,7847743232008148,77207807539770572,759807537336050712
%N Number of base 18 circular n-digit numbers with adjacent digits differing by 5 or less.
%C [Empirical] a(base,n)=a(base-1,n)+F(5) for base>=5.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]`-$[(i+1)mod N]`>5)+($[(i+1)mod N]`-$[i]`>5))
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006