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%I #8 Mar 31 2012 12:35:02
%S 1,21,259,2709,32627,401401,5043115,64108009,821245795,10571373945,
%T 136492942139,1765686281633,22868116742483,296391829451401,
%U 3843261172758763,49848967431027409,646678407486881219
%N Number of base 21 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
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