The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A001813

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A001813

Quadruple factorial numbers: a(n) = (2n)!/n!.
(history; published version)

#272 by Peter Luschny at Fri Sep 13 11:58:04 EDT 2024

STATUS

reviewed

approved

#271 by Joerg Arndt at Fri Sep 13 11:55:28 EDT 2024

STATUS

proposed

reviewed

#270 by Peter Luschny at Fri Sep 13 11:33:13 EDT 2024

STATUS

editing

proposed

#269 by Peter Luschny at Fri Sep 13 11:30:24 EDT 2024

FORMULA

a(n) = 1/([x^n] hypergeom([1], [1/2], x/4)). - Peter Luschny, Sep 13 2024

MAPLE

A001813 := n -> mul(k, k = select(k-> k mod 4 = 2, [$1 .. 4*n])): seq(A001813(n), n=0..16);

seq(A001813(n), n=0..16); # Peter Luschny, Jun 23 2011

STATUS

approved

editing

Discussion

Fri Sep 13

11:33

Peter Luschny: Let's make math simple again and represent everything as /hypergeoms/!

#268 by Peter Luschny at Fri Jul 21 15:50:15 EDT 2023

STATUS

reviewed

approved

#267 by Amiram Eldar at Fri Jul 21 15:47:39 EDT 2023

STATUS

proposed

reviewed

#266 by Neven Sajko at Fri Jul 21 15:41:22 EDT 2023

STATUS

editing

proposed

#265 by Neven Sajko at Fri Jul 21 15:20:01 EDT 2023

FORMULA

a(n) = 2*(2*n - 1)*a(n-1). - Neven Sajko, Jul 21 2023

STATUS

proposed

editing

#264 by Alois P. Heinz at Fri Jul 21 13:27:17 EDT 2023

STATUS

editing

proposed

#263 by Alois P. Heinz at Fri Jul 21 13:23:58 EDT 2023

DATA

1, 2, 12, 120, 1680, 30240, 665280, 17297280, 518918400, 17643225600, 670442572800, 28158588057600, 1295295050649600, 64764752532480000, 3497296636753920000, 202843204931727360000, 12576278705767096320000, 830034394580628357120000, 58102407620643984998400000

FORMULA

Recurrence: a(n) = 2*(2*n - 1)*a(n-1). - Neven Sajko, Jul 21 2023

STATUS

proposed

editing

Discussion

Fri Jul 21

13:27

Alois P. Heinz: there is already "a(n) = A016825(n-1)*a(n-1)." above, and 
A016825(n) = 4*n+2 ...