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%I #7 Mar 31 2012 12:35:06
%S 1,31,259,2211,19019,164343,1424235,12368115,107567215,936593437,
%T 8162112673,71178552195,621048996119,5421039243545,47334756754423,
%U 413416811445643,3611458265770503,31553302705135081,275714829055325817
%N Number of base 31 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 31 differing by three or less A126499, two or less A126418, one or less A126385.
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006
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