A001305 - OEIS

A001305

Expansion of 1/((1-x)^2*(1-x^2)*(1-x^5)*(1-x^10)*(1-x^20)).

1, 2, 4, 6, 9, 13, 18, 24, 31, 39, 50, 62, 77, 93, 112, 134, 159, 187, 218, 252, 293, 337, 388, 442, 503, 571, 646, 728, 817, 913, 1022, 1138, 1267, 1403, 1552, 1714, 1889, 2077, 2278, 2492, 2728, 2977, 3248, 3532, 3838, 4166, 4516, 4888, 5282, 5698, 6148

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OFFSET

0,2

LINKS

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

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 201

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

FORMULA

G.f.: 1/((1-x)^2*(1-x^2)*(1-x^5)*(1-x^10)*(1-x^20)).

MATHEMATICA

CoefficientList[Series[1/((1-x)^2*(1-x^2)*(1-x^5)*(1-x^10)*(1-x^20)), {x, 0, 50}], x] (* Vincenzo Librandi, Feb 24 2012 *)

PROG

(Maxima) a(n):=block([f:divide((1-z^20)^5, (1-z)^2*(1-z^2)*(1-z^5)*(1-z^10), z)[1]], return(sum(binomial(k+5, 5)*coeff(f, z, n-20*k), k, max(0, ceiling((n-81)/20)), floor(n/20)))); /* Tani Akinari, May 12 2014 */

CROSSREFS

Sequence in context: A177239 A001304 A000064 * A088575 A177189 A026906

Adjacent sequences: A001302 A001303 A001304 * A001306 A001307 A001308

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane

STATUS

approved