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A110903 Difference between the factorial of n and the double factorial of n. 3
0, 0, 0, 3, 16, 105, 672, 4935, 39936, 361935, 3624960, 39906405, 478955520, 6226885665, 87177646080, 1307672340975, 20922779566080, 355687393636575, 6402373519933440, 121645099754102925, 2432902004460748800, 51090942157960129425, 1124000727695858073600 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,4

LINKS

Andrew Howroyd, Table of n, a(n) for n = 0..200

FORMULA

a(n) = n! - n!!.

a(n) = A000142(n) - A006882(n). - Andrew Howroyd, Jan 02 2020

EXAMPLE

a(7) = 7*6*5*4*3*2*1 - 7*5*3*1 = 4935.

MATHEMATICA

Table[(n!-n!!), {n, 0, 15}] - Zerinvary Lajos, Mar 21 2007

PROG

(PARI) a(n)={n! - if(n%2, n!/((n\2)!*2^(n\2)), (n/2)!*2^(n/2))} \\ Andrew Howroyd, Jan 02 2020

CROSSREFS

Cf. A000142 (factorials), A006882 (double factorials).

Sequence in context: A207434 A074542 A105622 * A206351 A085614 A215931

Adjacent sequences:  A110900 A110901 A110902 * A110904 A110905 A110906

KEYWORD

easy,nonn

AUTHOR

Paolo P. Lava, Sep 21 2005

EXTENSIONS

Terms a(15) and beyond from Andrew Howroyd, Jan 02 2020

STATUS

approved

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Last modified January 28 00:32 EST 2020. Contains 331313 sequences. (Running on oeis4.)