

A179521


The number of (nontrivial) cycles in the symmetric group S_2n that involve equally many elements in {1,...,n} and {n+1,...,2n}.


1



0, 1, 10, 183, 7192, 501505, 54163866, 8349297775, 1738661539168, 469966765754097, 159953336512367770, 66922241946410591191, 33756538093718717040600, 20201172267759560773858513, 14150039840975130413592164362, 11468217024458648756976754157295
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OFFSET

0,3


LINKS

Alois P. Heinz, Table of n, a(n) for n = 0..200


FORMULA

a(n) = Sum_{k=1..n} (2k1)! binomial(n,k)^2.


MAPLE

a:= n> add((2*k1)!*binomial(n, k)^2, k=1..n):
seq(a(n), n=0..20); # Alois P. Heinz, Jun 14 2015


PROG

(PARI) a(n) = sum(k=1, n, (2*k1)! * binomial(n, k)^2); \\ Michel Marcus, Aug 14 2013


CROSSREFS

Sequence in context: A240405 A304936 A239764 * A211102 A121973 A223146
Adjacent sequences: A179518 A179519 A179520 * A179522 A179523 A179524


KEYWORD

nonn


AUTHOR

Lukas Brantner (dlbb2(AT)cam.ac.uk), Jul 17 2010


EXTENSIONS

More terms from Michel Marcus, Aug 14 2013


STATUS

approved



