A060377 Pepin's test numbers.

3, 9, 6561, 11790184577738583171520872861412518665678211592275841109096961

Offset

0,1

Comments

Next two terms have 15635 and 1024610093 digits respectively. [Corrected by Michael S. Branicky and Sean A. Irvine, Nov 12 2022]

Links

Table of n, a(n) for n=0..3.

C. K. Caldwell, Pepin's Test.

Formula

a(n) = 3^((F(n)-1)/2) where F(n) is a Fermat number (A000215).

Example

a(1) = 3^((F(1)-1)/2) = 3^((5-1)/2) = 3^2 = 9.

Mathematica

A000215[n_]:=2^(2^n)+1; a[n_]:=3^((A000215[n]-1)/2); Array[a, 4, 0] (* Stefano Spezia, Sep 14 2024 *)

Prog

(Python)
def a(n): return 3**(2**(2**n-1))
print([a(n) for n in range(4)]) # Michael S. Branicky, Nov 12 2022

Crossrefs

Cf. A000215.

Sequence in context: A060712 A122463 A072005 * A255503 A027896 A116620

Adjacent sequences: A060374 A060375 A060376 * A060378 A060379 A060380

Keyword

nonn

Author

Jason Earls, Apr 02 2001

Extensions

Corrected offset, formula and example Harry J. Smith, Jul 04 2009

Status

approved