login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A114854 a(n) = floor(n^(n/2)/n!!). 1
1, 1, 1, 2, 3, 4, 8, 10, 20, 26, 51, 64, 128, 163, 326, 416, 834, 1067, 2148, 2755, 5559, 7147, 14449, 18613, 37696, 48638, 98650, 127463, 258857, 334864, 680822, 881657, 1794294, 2325750, 4737361 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

This sequence is a second approximation of a double factorial analog to Stirling's approximation to factorial. Note that a(n) is exact for n = 1, 2, 4.

LINKS

Table of n, a(n) for n=1..35.

FORMULA

a(n) = floor(n^(n/2)/n!!). a(n) = floor(sqrt(A000312(n))/A006882(n)).

EXAMPLE

a(10) = floor((10^5)/3840) = floor(26.0416667) = 26.

a(11) = floor((11^5.5)/10395) = floor(51.3848715) = 51.

MAPLE

A114854 := proc(n)

    n^(n/2)/doublefactorial(n) ;

    floor(%) ;

end proc:

seq(A114854(n), n=1..35) ; # R. J. Mathar, Jun 23 2014

MATHEMATICA

Table[Floor[n^(n/2)/n!!], {n, 40}] (* Harvey P. Dale, Apr 04 2019 *)

CROSSREFS

Cf. A000312, A006882, A055775.

Sequence in context: A295296 A186417 A207644 * A127279 A106131 A275646

Adjacent sequences:  A114851 A114852 A114853 * A114855 A114856 A114857

KEYWORD

easy,nonn

AUTHOR

Jonathan Vos Post, Feb 20 2006

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified March 2 19:18 EST 2021. Contains 341756 sequences. (Running on oeis4.)