%I #8 Mar 31 2012 12:35:02
%S 1,28,442,5878,90262,1415878,22695076,368310712,6028038286,
%T 99207708814,1638704629522,27132638036202,449943629944228,
%U 7468996856620028,124065300876811890,2061684054575682598,34269888230469320798
%N Number of base 28 circular n-digit numbers with adjacent digits differing by 9 or less.
%C [Empirical] a(base,n)=a(base-1,n)+F(9) for base>=9.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]`-$[(i+1)mod N]`>9)+($[(i+1)mod N]`-$[i]`>9))
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006