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A254866 a(n) = (n!!)^n. 2
1, 1, 4, 27, 4096, 759375, 12230590464, 140710042265625, 472769874482845188096, 601016336033894136931640625, 697127546117424200558837760000000000, 153133225508583375568553948649382367138671875, 91653624689233987245068783089656480594395136000000000000 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
LINKS
Eric Weisstein, Double Factorial, (MathWorld)
FORMULA
a(n) ~ Pi^(n/2) * n^(n*(n+1)/2) / exp(n^2/2 - 1/6) if n is even.
a(n) ~ 2^(n/2) * n^(n*(n+1)/2) / exp(n^2/2 - 1/6) if n is odd.
MATHEMATICA
Table[(n!!)^n, {n, 0, 15}]
CROSSREFS
Sequence in context: A132641 A008973 A132646 * A292968 A000869 A132640
KEYWORD
nonn,easy
AUTHOR
Vaclav Kotesovec, Feb 19 2015
STATUS
approved

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Last modified April 17 08:05 EDT 2024. Contains 371756 sequences. (Running on oeis4.)