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A126504 Number of base 9 n-digit numbers with adjacent digits differing by four or less. 2
1, 9, 61, 429, 3011, 21141, 148433, 1042167, 7317185, 51374875, 360709449, 2532586341, 17781606753, 124846894103, 876565722303, 6154478019155, 43211363078111, 303392406838867, 2130156189729353, 14956094122197975 (list; graph; refs; listen; history; text; internal format)
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.

LINKS

Table of n, a(n) for n=0..19.

FORMULA

Conjectures from Colin Barker, Jun 01 2017: (Start)

G.f.: (1 - x)*(1 + 3*x - x^3) / (1 - 7*x - x^2 + 6*x^3 - x^5).

a(n) = 7*a(n-1) + a(n-2) - 6*a(n-3) + a(n-5) for n>5.

(End)

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 9 differing by three or less A126477, two or less A126396, one or less A126363.

Sequence in context: A243877 A200674 A162769 * A025014 A246567 A322086

Adjacent sequences:  A126501 A126502 A126503 * A126505 A126506 A126507

KEYWORD

nonn,base

AUTHOR

R. H. Hardin, Dec 28 2006

STATUS

approved

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Last modified May 7 16:00 EDT 2021. Contains 343652 sequences. (Running on oeis4.)