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A129441 G.f. x*(1-x^2-x^3)/ ((1+x+x^2) * (x^4-x^3-x^2-2*x+1) ). 0
1, 1, 2, 7, 16, 39, 100, 248, 618, 1546, 3858, 9631, 24049, 60041, 149903, 374266, 934427, 2332981, 5824753, 14542648, 36308602, 90651625, 226329747, 565077072, 1410826915, 3522409024, 8794392287, 21956943442, 54819861280, 136868649264 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

The case q=1 on page 132 of the Billey et al. paper.

LINKS

Table of n, a(n) for n=1..30.

Sara Billey, Gregory Warrington, Kazhdan-Lusztig Polynomials for 321-hexagon-avoiding permutations, J. Algebr. Combinat. 13 (2) (2001) 111-136.

Index entries for linear recurrences with constant coefficients, signature (1, 2, 4, 1, 0, -1).

FORMULA

a(n) = a(n-1) +2*a(n-2) +4*a(n-3) +a(n-4) -a(n-6).

MATHEMATICA

p[x_, q_] = (-1 + q^2*x^2 + q^3*x^3)/((1 + q*x + q^2*x^2)*(-1 + x + q*x + q^2*x^2 + q^2*x^3 - q^4*x^4)); Table[ SeriesCoefficient[Series[p[x, 1], {x, 0, 30}], n], {n, 0, 30}]

LinearRecurrence[{1, 2, 4, 1, 0, -1}, {1, 1, 2, 7, 16, 39}, 40] (* Harvey P. Dale, Nov 26 2015 *)

CROSSREFS

Sequence in context: A042243 A293378 A041887 * A093971 A065497 A131727

Adjacent sequences:  A129438 A129439 A129440 * A129442 A129443 A129444

KEYWORD

nonn

AUTHOR

Roger L. Bagula, Jun 08 2007

EXTENSIONS

Definition simplified - the Assoc. Eds of the OEIS, Mar 28 2010

STATUS

approved

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Last modified October 23 21:57 EDT 2019. Contains 328373 sequences. (Running on oeis4.)