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%I #8 Mar 31 2012 12:35:02
%S 1,20,290,3710,53630,790670,11804384,177140396,2664526934,40121436206,
%T 604415162550,9107184376046,137237515952000,2068136987970632,
%U 31166901568081520,469690150305370760,7078330364431520854
%N Number of base 20 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
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