A174212 Ultradoublefactorials: a(n) = (n!!)^(n!!).

1, 1, 4, 27, 16777216, 437893890380859375, 500702078263459319174537025249570888246709955377400223021257741084821677152403456

Offset

0,3

Comments

The next term (a(8)) has 993 digits. - Harvey P. Dale, Aug 17 2017

Links

Table of n, a(n) for n=0..6.

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

Cf. A006882, A046882, A134877, A165812.

Sequence in context: A132640 A307031 A306823 * A352838 A038706 A358863

Adjacent sequences: A174209 A174210 A174211 * A174213 A174214 A174215

Keyword

easy,nonn

Author

Paolo P. Lava & Giorgio Balzarotti, Mar 16 2010

Status

approved