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Search: id:A099581
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| A099581 |
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Sum C(n-k,k-1)3^(n-k-1), k=0..floor(n/2). |
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+0
2
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| 0, 0, 1, 3, 15, 54, 216, 810, 3105, 11745, 44631, 169128, 641520, 2431944, 9221121, 34959195, 132543135, 502506990, 1905156936, 7222991778, 27384465825, 103822372809, 393620574951, 1492328843280, 5657848431840, 21450531825360
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OFFSET
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0,4
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COMMENT
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In general a(n)=sum{k=0..floor(n/2), C(n-k,k-1)r^(n-k-1) has g.f. x^2/((1-r*x^2)(1-r*x-r*x^2)) and satisfies a(n)=r*a(n-1)+2r*a(n-2)-r^2*a(n-3)-r^2*a(n-4).
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FORMULA
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G.f.: x^2/((1-3x^2)(1-3x-3x^2)); a(n)=3a(n-1)+6a(n-2)-9a(n-3)-9a(n-4).
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CROSSREFS
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Cf. A099177, A099582.
Sequence in context: A038192 A147618 A085480 this_sequence A026696 A082708 A093925
Adjacent sequences: A099578 A099579 A099580 this_sequence A099582 A099583 A099584
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Oct 23 2004
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