A139802 a(1)=1, a(2)=2, a(n)=n^a(n-2).

1, 2, 3, 16, 125, 2821109907456, 4337654948097993282537354757263188251697832994620405101744893017744569432720994168089672192211758909320807

Offset

1,2

Comments

Exponential double factorial.

The next term is too large to include.

Links

Table of n, a(n) for n=1..7.

Example

a(1)=1;
a(2)=2;
a(3)=3^1=3;
a(4)=4^2=16;
a(5)=5^3=125;
a(6)=6^16=2821109907456;
etc.

Mathematica

a[1]=1; a[2]=2; a[n_]:=n^a[n-2]; Array[a, 7] (* Stefano Spezia, Feb 14 2024 *)

Crossrefs

Cf. A049384.

Sequence in context: A269067 A370201 A356882 * A292207 A063666 A006247

Adjacent sequences: A139799 A139800 A139801 * A139803 A139804 A139805

Keyword

easy,nonn

Author

Paolo P. Lava and Giorgio Balzarotti, May 22 2008

Status

approved