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A099623
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Sum C(n-k,k+2)2^(n-k-2)(3/2)^k, k=0..floor(n/2).
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2
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0, 0, 1, 6, 27, 104, 369, 1242, 4039, 12828, 40077, 123758, 379011, 1153872, 3498025, 10572354, 31884543, 96010436, 288788613, 867967830, 2607282235, 7828953720, 23501774241, 70536546986, 211674885687, 635160738924, 1905765565309
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,4
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COMMENTS
| In general a(n)=sum{k=0..floor(n/2), C(n-k,k+2)u^(n-k-2)(v/u)^k has g.f. x^2/((1-u*x)^2(1-u*x-v*x^2)) and satisfies the recurrence a(n)=3u*a(n-1)-(3u^2-v)a(n-2)+(u^3-2uv)a(n-3)+u^2^v*a(n-4).
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FORMULA
| G.f.: x^2/((1-2x)^2(1-2x-3x^2)); a(n)=6a(n-1)-9a(n-2)-4a(n-3)+12a(n-4).
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CROSSREFS
| Sequence in context: A054457 A000395 A005325 * A119852 A027471 A037695
Adjacent sequences: A099620 A099621 A099622 * A099624 A099625 A099626
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Oct 25 2004
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