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%I #9 Jul 18 2017 11:30:41
%S 1,18,114,742,4874,32186,213226,1415510,9409592,62605198,416772336,
%T 2775553058,18488673878,123177305178,820730049614,5468888194572,
%U 36443213300730,242854735692378,1618394841578240,10785184848010492
%N Number of base 18 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+7*x-58*x^2-12*x^3+169*x^4-3*x^5-128*x^6+3*x^7+24*x^8) / (1-11*x+26*x^2+32*x^3-83*x^4-21*x^5+64*x^6+3*x^7-12*x^8) (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 18 differing by two or less A126405, one or less A126372.
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 27 2006
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