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%I #10 Jul 18 2017 08:02:41
%S 1,13,97,753,5897,46287,363509,2855151,22426249,176152007,1383628073,
%T 10868042671,85365689641,670525630751,5266807148873,41369421713583,
%U 324946216030489,2552369333410047,20048207650685929,157473538310505327
%N Number of base 13 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.
%F G.f.: (1+4*x-14*x^2-16*x^3+22*x^4+8*x^5-8*x^6) / (1-9*x+6*x^2+26*x^3-18*x^4-12*x^5+8*x^6) (conjectured). - _Colin Barker_, Jul 18 2017
%o (S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-2](($[i]`-$[i+1]`>4)+($[i+1]`-$[i]`>4))
%Y Cf. Base 13 differing by three or less A126481, two or less A126400, one or less A126367.
%K nonn,base
%O 0,2
%A _R. H. Hardin_, Dec 28 2006