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A114854
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a(n) = floor(n^(n/2)/n!!).
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1
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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
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OFFSET
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1,4
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COMMENTS
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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.
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LINKS
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Table of n, a(n) for n=1..35.
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FORMULA
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a(n) = floor(n^(n/2)/n!!). a(n) = floor(sqrt(A000312(n))/A006882(n)).
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EXAMPLE
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a(10) = floor((10^5)/3840) = floor(26.0416667) = 26.
a(11) = floor((11^5.5)/10395) = floor(51.3848715) = 51.
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MAPLE
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A114854 := proc(n)
n^(n/2)/doublefactorial(n) ;
floor(%) ;
end proc:
seq(A114854(n), n=1..35) ; # R. J. Mathar, Jun 23 2014
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MATHEMATICA
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Table[Floor[n^(n/2)/n!!], {n, 40}] (* Harvey P. Dale, Apr 04 2019 *)
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CROSSREFS
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Cf. A000312, A006882, A055775.
Sequence in context: A295296 A186417 A207644 * A127279 A106131 A275646
Adjacent sequences: A114851 A114852 A114853 * A114855 A114856 A114857
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KEYWORD
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easy,nonn
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AUTHOR
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Jonathan Vos Post, Feb 20 2006
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STATUS
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approved
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