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A114853 a(n) = floor(n^n/n!!). 1
1, 2, 9, 32, 208, 972, 7843, 43690, 409968, 2604166, 27447010, 193491763, 2241278030, 17224712961, 216027868615, 1787142709274, 24006211998207, 211773735868781, 3021737893128258, 28218694885361552, 424936725846414486 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

This is to double factorial A006882 as A055775 "Floor(n^n/n!)" is to factorial. This sequence is a weak first approximation of a double factorial analog to Stirling's approximation to factorial. Note that a(n) is exact for n = 1, 2, 3, 4, 6.

LINKS

Table of n, a(n) for n=1..21.

FORMULA

a(n) = floor(n^n/n!!). a(n) = floor(A000312(n)/A006882(n)).

EXAMPLE

a(10) = floor((10^10)/3840) = floor(2604166.67) = 2604166.

MAPLE

A114853 := proc(n)

    n^n/doublefactorial(n) ;

    floor(%) ;

end proc:

seq(A114853(n), n=1..25) ; # R. J. Mathar, Jun 23 2014

CROSSREFS

Cf. A000312, A006882, A055775.

Sequence in context: A150920 A013501 A179230 * A331727 A110376 A335577

Adjacent sequences:  A114850 A114851 A114852 * A114854 A114855 A114856

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Feb 20 2006

STATUS

approved

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Last modified February 25 19:39 EST 2021. Contains 341618 sequences. (Running on oeis4.)