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A099579
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Sum C(n-k,k-1)3^(k-1), k=0..floor(n/2).
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1
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0, 0, 1, 1, 7, 10, 40, 70, 217, 427, 1159, 2440, 6160, 13480, 32689, 73129, 173383, 392770, 919480, 2097790, 4875913, 11169283, 25856071, 59363920, 137109280, 315201040, 727060321, 1672663441, 3855438727, 8873429050, 20444528200
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,5
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COMMENTS
| In general a(n)=sum{k=0..floor(n/2), C(n-k,k-1)r^(k-1)} has g.f. x^2/((1-r*x^2)(1-x-r*x^2)) and satisfies the recurrence a(n)=a(n-1)+2r*a(n-2)-r*a(n-3)-r^2*a(n-4).
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FORMULA
| G.f.: x^2/((1-3x^2)(1-x-3x^2)); a(n)=a(n-1)+6a(n-2)-3a(n-3)-9a(n-4).
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CROSSREFS
| Cf. A097038, A099580.
Sequence in context: A119169 A095756 A126076 * A056521 A056510 A013398
Adjacent sequences: A099576 A099577 A099578 * A099580 A099581 A099582
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KEYWORD
| easy,nonn
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AUTHOR
| Paul Barry (pbarry(AT)wit.ie), Oct 23 2004
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