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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
OFFSET
0,4
LINKS
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: A368934 A344216 A105622 * A206351 A085614 A215931
KEYWORD
easy,nonn
AUTHOR
Paolo P. Lava, Sep 21 2005
EXTENSIONS
Terms a(15) and beyond from Andrew Howroyd, Jan 02 2020
STATUS
approved