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A099624
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Sum C(n-k,k+2)3^(n-k-2)(4/3)^k, k=0..floor(n/2).
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1
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0, 0, 1, 9, 58, 318, 1591, 7503, 33976, 149436, 643261, 2724357, 11395654, 47210154, 194121811, 793526571, 3228811492, 13090123272, 52917410041, 213437246145, 859342367890, 3455021317590, 13875655896751, 55677180731079
(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/((1-3x)^2(1-3x-4x^2)); a(n)=9a(n-1)-23a(n-2)+3a(n-3)+36a(n-4).
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CROSSREFS
| Cf. A099623.
Sequence in context: A044147 A044528 A027174 * A018218 A026750 A009034
Adjacent sequences: A099621 A099622 A099623 * A099625 A099626 A099627
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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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