A052645 - OEIS

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A052645

E.g.f. 2*x^2*(1+x-x^2)/(1-x).

0, 0, 4, 24, 48, 240, 1440, 10080, 80640, 725760, 7257600, 79833600, 958003200, 12454041600, 174356582400, 2615348736000, 41845579776000, 711374856192000, 12804747411456000, 243290200817664000

(list; graph; refs; listen; history; text; internal format)

OFFSET

0,3

LINKS

Table of n, a(n) for n=0..19.

INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 591

FORMULA

E.g.f.: 2*x^2*(-x+x^2-1)/(-1+x)

Recurrence: {a(1)=0, a(0)=0, (-1-n)*a(n)+a(n+1)=0, a(2)=4, a(3)=24, a(4)=48}

2*n!, n>3.

MAPLE

spec := [S, {S=Prod(Z, Union(Z, Z), Union(Z, Sequence(Z)))}, labeled]: seq(combstruct[count](spec, size=n), n=0..20);