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A174212 Ultradoublefactorials: a(n) = (n!!)^(n!!). 0
1, 1, 4, 27, 16777216, 437893890380859375, 500702078263459319174537025249570888246709955377400223021257741084821677152403456 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,3
COMMENTS
The next term (a(8)) has 993 digits. - Harvey P. Dale, Aug 17 2017
LINKS
FORMULA
a(n) = A006882(n)^A006882(n).
Sum_{n>=1} 1/a(n) = A134877. - Amiram Eldar, Nov 11 2020
EXAMPLE
For n=4 the doublefactorial is n!! = 4*2 = 8 and a(n) = n!!^n!! = 8^8 = 16777216.
MAPLE
P:=proc(i) local a, n; for n from 0 by 1 to i do print(doublefactorial(n)^doublefactorial(n)); od; end: P(10);
MATHEMATICA
udf[n_]:=Module[{c=n!!}, c^c]; Array[udf, 7, 0] (* Harvey P. Dale, Aug 17 2017 *)
CROSSREFS
Sequence in context: A132640 A307031 A306823 * A352838 A038706 A358863
KEYWORD
easy,nonn
AUTHOR
STATUS
approved

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Last modified May 23 16:36 EDT 2024. Contains 372765 sequences. (Running on oeis4.)