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A108486
Sum binomial(2n-2k,2k)3^k*2^(n-k), k=0..floor(n/2).
2
1, 2, 10, 80, 412, 2456, 14680, 85376, 503056, 2959136, 17381536, 102199040, 600757696, 3531251072, 20758107520, 122021457920, 717273440512, 4216334967296, 24784750512640, 145691471876096, 856414086962176
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).
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
Sequence in context: A245903 A100248 A368951 * A152168 A003578 A274276
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jun 04 2005
STATUS
approved