A108486 a(n) = Sum_{k=0..floor(n/2)} binomial(2n-2k,2k)3^k*2^(n-k).

1, 2, 10, 80, 412, 2456, 14680, 85376, 503056, 2959136, 17381536, 102199040, 600757696, 3531251072, 20758107520, 122021457920, 717273440512, 4216334967296, 24784750512640, 145691471876096, 856414086962176, 5034234076338176, 29592593307621376, 173953290940743680

Offset

0,2

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

Seiichi Manyama, Table of n, a(n) for n = 0..1000

Index entries for linear recurrences with constant coefficients, signature (4,8,24,-36).

Formula

G.f.: (1-2x-6x^2)/(1-4x-8x^2-24x^3+36x^4).

a(n) = 4a(n-1) + 8a(n-2) + 24a(n-3) - 36a(n-4).

Crossrefs

Cf. A390619.

Sequence in context: A245903 A100248 A368951 * A152168 A379383 A003578

Adjacent sequences: A108483 A108484 A108485 * A108487 A108488 A108489

Keyword

easy,nonn

Author

Paul Barry, Jun 04 2005

Status

approved