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A111308 Sum_{k=1..n} k!! * (n+1-k)!!, where k!! = k*(k-2)*(k-4)..*(1 or 2). 1
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; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..25.

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.

MATHEMATICA

Table[ Sum[k!!(n + 1 - k)!!, {k, n}], {n, 25}] (* Robert G. Wilson v *)

CROSSREFS

Cf. A006882.

Sequence in context: A274597 A335548 A203293 * A121302 A026150 A026123

Adjacent sequences:  A111305 A111306 A111307 * A111309 A111310 A111311

KEYWORD

easy,nonn

AUTHOR

Leroy Quet, Nov 03 2005

EXTENSIONS

More terms from Robert G. Wilson v, Nov 04 2005

STATUS

approved

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Last modified August 4 09:03 EDT 2020. Contains 336201 sequences. (Running on oeis4.)