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%I #12 Jun 02 2017 12:59:50
%S 1,9,75,597,4999,41959,352605,2963557,24908879,209361909,1759712475,
%T 14790602187,124316856469,1044898695889,8782503978435,73818042322837,
%U 620449861007519,5214958537443999,43832377531943085,368416605100242957
%N Number of base 9 circular n-digit numbers with adjacent digits differing by 6 or less.
%C [Empirical] a(base,n)=a(base-1,n)+F(6) for base>=6.int(n/2)+1 and F(d) is the largest coefficient in (1+x+...+x^(2d))^n
%F G.f.: (1 - 3*x^2 - 34*x^3 + 3*x^4 + 20*x^5) / ((1 + x)*(1 - x - x^2)*(1 - 9*x + 5*x^2)) (conjectured). - _Colin Barker_, Jun 02 2017
%o (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-1](($[i]`-$[(i+1)mod N]`>6)+($[(i+1)mod N]`-$[i]`>6))
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006