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A078026 Expansion of (1-x)/(1-x^2-2*x^3). 0
1, -1, 1, 1, -1, 3, 1, 1, 7, 3, 9, 17, 15, 35, 49, 65, 119, 163, 249, 401, 575, 899, 1377, 2049, 3175, 4803, 7273, 11153, 16879, 25699, 39185, 59457, 90583, 137827, 209497, 318993, 485151, 737987, 1123137, 1708289, 2599111, 3954563, 6015689, 9152785, 13924815 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

LINKS

Table of n, a(n) for n=0..44.

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

FORMULA

a(n) = sum(m=1..n, sum(i=0..n-m, binomial(m+i-1,m-1)*sum(j=0..m, binomial(j,n-3*m+2*j-i)*2^(m-j)*binomial(m,j)*(-1)^(-n+3*m-j+i)))); [Vladimir Kruchinin, May 12 2011]

MATHEMATICA

CoefficientList[Series[(1 - x)/(1 - x^2 - 2*x^3), {x, 0, 50}], x] (* Wesley Ivan Hurt, Jan 24 2017 *)

PROG

(Maxima)

a(n):=sum(sum(binomial(m+i-1, m-1)*sum(binomial(j, n-3*m+2*j-i)*2^(m-j)*binomial(m, j)*(-1)^(-n+3*m-j+i), j, 0, m), i, 0, n-m), m, 1, n); /* Vladimir Kruchinin, May 12 2011 */

(PARI) Vec((1-x)/(1-x^2-2*x^3) + O(x^45)) \\ Felix Fröhlich, Jan 24 2017

CROSSREFS

Sequence in context: A228524 A116407 A135288 * A126713 A140068 A179745

Adjacent sequences:  A078023 A078024 A078025 * A078027 A078028 A078029

KEYWORD

sign,easy

AUTHOR

N. J. A. Sloane, Nov 17 2002

STATUS

approved

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Last modified January 17 23:15 EST 2019. Contains 319251 sequences. (Running on oeis4.)