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A108484
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Sum binomial(2n-2k,2k)3^k, k=0..floor(n/2).
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1
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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; internal format)
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OFFSET
| 0,3
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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).
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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).
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CROSSREFS
| Sequence in context: A122681 A174612 A020496 * A134507 A098813 A055485
Adjacent sequences: A108481 A108482 A108483 * A108485 A108486 A108487
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Jun 04 2005
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