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

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

Offset: 0

Author

Paolo P. Lava & Giorgio Balzarotti, Mar 16 2010

Keywords

• easy
• nonn

Comments

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

Examples

			For n=4 the doublefactorial is n!! = 4*2 = 8 and a(n) = n!!^n!! = 8^8 = 16777216.
		

Crossrefs

Cf. A006882, A046882, A134877, A165812.

Programs

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 *)

Formula

a(n) = A006882(n)^A006882(n).

Sum_{n>=1} 1/a(n) = A134877. - Amiram Eldar, Nov 11 2020