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%I #8 Jul 19 2017 09:39:38
%S 1,20,128,840,5560,36988,246840,1650808,11056590,74130748,497387482,
%T 3339002940,22423219250,150623072388,1011962290858,6799752144942,
%U 45694220498130,307084056184964,2063824981953422,13870824556736138
%N Number of base 20 n-digit numbers with adjacent digits differing by three or less.
%C [Empirical] a(base,n)=a(base-1,n)+7^(n-1) for base>=3n-2; a(base,n)=a(base-1,n)+7^(n-1)-2 when base=3n-3.
%F G.f.: (1+9*x-69*x^2-55*x^3+242*x^4+192*x^5-94*x^6-73*x^7+5*x^8+4*x^9) / (1-11*x+23*x^2+53*x^3-82*x^4-100*x^5+30*x^6+35*x^7-x^8-2*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]`-$[i+1]`>3)+($[i+1]`-$[i]`>3))
%Y Cf. Base 20 differing by two or less A126407, one or less A126374.
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 27 2006
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