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%I #7 Mar 31 2012 12:35:06
%S 1,26,214,1806,15374,131538,1128990,9710910,83652388,721363974,
%T 6225222156,53750847042,464278918952,4011329573242,34664086928592,
%U 299591386800116,2589524785835700,22384118655449566,193499832018326518
%N Number of base 26 n-digit numbers with adjacent digits differing by four or less.
%C [Empirical] a(base,n)=a(base-1,n)+9^(n-1) for base>=4n-3; a(base,n)=a(base-1,n)+9^(n-1)-2 when base=4n-4
%o (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-2](($[i]`-$[i+1]`>4)+($[i+1]`-$[i]`>4))
%Y Cf. Base 26 differing by three or less A126494, two or less A126413, one or less A126380.
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006
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