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A126510
Number of base 15 n-digit numbers with adjacent digits differing by four or less.
1
1, 15, 115, 915, 7355, 59369, 479887, 3880945, 31391483, 253929457, 2054110259, 16616430593, 134416594859, 1087347726489, 8795978441155, 71154097145873, 575593242083915, 4656198285106057, 37665804590772499, 304693389569808737
OFFSET
0,2
COMMENTS
[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.
FORMULA
G.f.: (1+6*x-18*x^2-48*x^3-6*x^4+24*x^5+8*x^6) / (1-9*x+2*x^2+42*x^3+14*x^4-20*x^5-8*x^6) (conjectured). - Colin Barker, Jul 18 2017
PROG
(S/R) stvar $[N]:(0..M-1) init $[]:=0 asgn $[]->{*} kill +[i in 0..N-2](($[i]`-$[i+1]`>4)+($[i+1]`-$[i]`>4))
CROSSREFS
Cf. Base 15 differing by three or less A126483, two or less A126402, one or less A126369.
Sequence in context: A044728 A091347 A125352 * A328725 A331211 A183475
KEYWORD
nonn,base
AUTHOR
R. H. Hardin, Dec 28 2006
STATUS
approved