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%I #9 Jul 19 2017 07:42:31
%S 1,20,58,170,500,1474,4352,12864,38058,112674,333776,989236,2933102,
%T 8699864,25812862,76609418,227424420,675289026,2005535520,5957318820,
%U 17698806798,52590044172,156287402420,464515721050,1380792800096
%N Number of base 20 n-digit numbers with adjacent digits differing by one or less.
%C [Empirical] a(base,n)=a(base-1,n)+3^(n-1) for base>=n; a(base,n)=a(base-1,n)+3^(n-1)-2 when base=n-1.
%F G.f.: (1+9*x-117*x^2+356*x^3-266*x^4-399*x^5+546*x^6+82*x^7-216*x^8+x^9+12*x^10) / ((1-2*x)*(1-4*x+3*x^2+x^3)*(1-5*x+4*x^2+8*x^3-5*x^4-3*x^5+x^6)) (conjectured). - _Colin Barker_, Jul 18 2017
%o (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-2](($[i]`-$[i+1]`>1)+($[i+1]`-$[i]`>1))
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 26 2006
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