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A108484 Sum binomial(2n-2k,2k)3^k, k=0..floor(n/2). 1
1, 1, 4, 19, 55, 220, 793, 2845, 10480, 37963, 138259, 503608, 1831969, 6669865, 24276892, 88362451, 321640831, 1170726484, 4261339801, 15510894949, 56458080328, 205502135851, 748007984827, 2722677076336, 9910284168961 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

COMMENTS

In general, sum{k=0..floor(n/2), C(2n-2k,2k)a^k*b^(n-k)} has expansion (1-bx-abx^2)/(1-2bx-(2ab-b^2)x^2-2ab^2*x^3+(ab)^2*x^4).

LINKS

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

Index entries for linear recurrences with constant coefficients, signature (2,5,6,-9).

FORMULA

G.f.: (1-x-3x^2)/(1-2x-5x^2-6x^3+9x^4); a(n)=2a(n-1)+5a(n-2)+6a(n-3)-9a(n-4).

CROSSREFS

Sequence in context: A215862 A174612 A020496 * A283333 A332697 A134507

Adjacent sequences:  A108481 A108482 A108483 * A108485 A108486 A108487

KEYWORD

easy,nonn

AUTHOR

Paul Barry, Jun 04 2005

STATUS

approved

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Last modified April 6 12:19 EDT 2020. Contains 333273 sequences. (Running on oeis4.)