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A097662 a(n) = A002720(n) - 1. 2
0, 1, 6, 33, 208, 1545, 13326, 130921, 1441728, 17572113, 234662230, 3405357681, 53334454416, 896324308633, 16083557845278, 306827170866105, 6199668952527616, 132240988644215841, 2968971263911288998, 69974827707903049153, 1727194482044146637520, 44552237162692939114281 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

LINKS

Table of n, a(n) for n=0..21.

FORMULA

a(n) = Sum_{k=1...n} (n!^2 / k!(n-k)!^2).

a(n) = Sum_{k=1...n} P(n, k)C(n, k) where P(n,k), are the permutation coefficients A008279.

a(n) = n*A129833(n-1) for n>=1. - Peter Luschny, Oct 11 2016

EXAMPLE

a(2) = 6 because A002720(2) = 7 and 7 - 1 = 6.

MAPLE

a := n -> hypergeom([-n, -n], [], 1) - 1:

seq(simplify(a(n)), n=0..26); # Peter Luschny, Oct 11 2016

CROSSREFS

Cf. A002720, A008279, A129833.

Main diagonal of A329655.

Sequence in context: A218182 A093964 A193665 * A277485 A012522 A012326

Adjacent sequences:  A097659 A097660 A097661 * A097663 A097664 A097665

KEYWORD

nonn

AUTHOR

Ross La Haye, Sep 20 2004

STATUS

approved

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Last modified March 29 17:23 EDT 2020. Contains 333116 sequences. (Running on oeis4.)