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%I #9 Jul 18 2017 11:30:32
%S 1,18,52,152,446,1312,3866,11406,33684,99552,294410,871138,2578808,
%T 7636982,22624216,67043480,198726606,589195584,1747255194,5182477842,
%U 15374283866,45616475418,135366696658,401753608184,1192506493748
%N Number of base 18 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+8*x-92*x^2+231*x^3-91*x^4-281*x^5+202*x^6+87*x^7-51*x^8-5*x^9) / (1-10*x+36*x^2-49*x^3-7*x^4+69*x^5-30*x^6-21*x^7+9*x^8+x^9) (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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