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A143459 Expansion of 1/(x^k*(1-x-3*x^(k+1))) for k=8. 2
1, 4, 7, 10, 13, 16, 19, 22, 25, 28, 40, 61, 91, 130, 178, 235, 301, 376, 460, 580, 763, 1036, 1426, 1960, 2665, 3568, 4696, 6076, 7816, 10105, 13213, 17491, 23371, 31366, 42070, 56158, 74386, 97834, 128149, 167788, 220261, 290374, 384472, 510682 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

a(n) is also the number of length n quaternary words with at least 8 0-digits between any other digits.

LINKS

Vincenzo Librandi, Table of n, a(n) for n = 0..1000

FORMULA

G.f.: 1/(x^8*(1-x-3*x^9)).

MAPLE

a := proc(k::nonnegint) local n, i, j; if k=0 then unapply (4^n, n) else unapply ((Matrix(k+1, (i, j)-> if (i=j-1) or j=1 and i=1 then 1 elif j=1 and i=k+1 then 3 else 0 fi)^(n+k))[1, 1], n) fi end(8): seq (a(n), n=0..58);

MATHEMATICA

Series[1/(1-x-3*x^9), {x, 0, 58}] // CoefficientList[#, x]& // Drop[#, 8]& (* Jean-François Alcover, Feb 13 2014 *)

CROSSREFS

8th column of A143461.

Sequence in context: A143460 A338701 A310679 * A143458 A004084 A121381

Adjacent sequences: A143456 A143457 A143458 * A143460 A143461 A143462

KEYWORD

nonn,easy

AUTHOR

Alois P. Heinz, Aug 16 2008

STATUS

approved

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Last modified December 5 12:01 EST 2022. Contains 358586 sequences. (Running on oeis4.)