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%I #9 Jul 19 2017 07:42:45
%S 1,21,61,179,527,1555,4595,13593,40245,119235,353459,1048285,3110249,
%T 9231305,27407185,81392387,241773327,718335747,2134675683,6344739309,
%U 18861068265,56076828573,166747755621,495896780609,1474935978225
%N Number of base 21 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+10*x-126*x^2+366*x^3-166*x^4-700*x^5+679*x^6+426*x^7-466*x^8-104*x^9+73*x^10+6*x^11) / ((1-x)*(1-10*x+34*x^2-32*x^3-54*x^4+100*x^5+23*x^6-76*x^7-10*x^8+12*x^9+x^10)) (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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