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A126374 Number of base 20 n-digit numbers with adjacent digits differing by one or less. 4
1, 20, 58, 170, 500, 1474, 4352, 12864, 38058, 112674, 333776, 989236, 2933102, 8699864, 25812862, 76609418, 227424420, 675289026, 2005535520, 5957318820, 17698806798, 52590044172, 156287402420, 464515721050, 1380792800096 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

[Empirical] a(base,n)=a(base-1,n)+3^(n-1) for base>=n; a(base,n)=a(base-1,n)+3^(n-1)-2 when base=n-1.

LINKS

Table of n, a(n) for n=0..24.

FORMULA

G.f.: (1+9*x-117*x^2+356*x^3-266*x^4-399*x^5+546*x^6+82*x^7-216*x^8+x^9+12*x^10) / ((1-2*x)*(1-4*x+3*x^2+x^3)*(1-5*x+4*x^2+8*x^3-5*x^4-3*x^5+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]`-$[i+1]`>1)+($[i+1]`-$[i]`>1))

CROSSREFS

Sequence in context: A104100 A069132 A124713 * A229536 A220013 A220046

Adjacent sequences:  A126371 A126372 A126373 * A126375 A126376 A126377

KEYWORD

nonn,base

AUTHOR

R. H. Hardin, Dec 26 2006

STATUS

approved

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Last modified September 24 01:21 EDT 2020. Contains 337315 sequences. (Running on oeis4.)