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A111308
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Sum_{k=1..n} k!! * (n+1-k)!!, where k!! = k*(k-2)*(k-4)..*(1 or 2).
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0
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0, 1, 4, 10, 28, 71, 204, 556, 1716, 5049, 16884, 53418, 193500, 654639, 2560140, 9209016, 38697300, 147193425, 661035060, 2645445870, 12627252540, 52926443415, 267088884300, 1167777120420, 6200158778100, 28178714373705
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,3
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EXAMPLE
| a(5) = 1 *5*3*1 + 2 *4*2 + 3*1 *3*1 + 4*2 *2 + 5*3*1 *1 = 15 + 16 + 9 + 16 + 15 = 71.
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MATHEMATICA
| Table[ Sum[k!!(n + 1 - k)!!, {k, n}], {n, 25}] (* Robert G. Wilson v *)
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CROSSREFS
| Cf. A006882.
Sequence in context: A133726 A026534 A203293 * A121302 A026150 A026123
Adjacent sequences: A111305 A111306 A111307 * A111309 A111310 A111311
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KEYWORD
| easy,nonn
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AUTHOR
| Leroy Quet Nov 03 2005
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(at)rgwv.com), Nov 04 2005
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