A152153 Positive residues of Pepin's Test for Fermat numbers using the base 3.

0, 4, 16, 256, 65536, 10324303, 11860219800640380469, 110780954395540516579111562860048860420, 5864545399742183862578018016183410025465491904722516203269973267547486512819

Offset

0,2

Comments

For n>=1 the Fermat Number F(n) is prime if and only if 3^((F(n) - 1)/2) is congruent to -1 (mod F(n)).

References

M. Krizek, F. Luca & L. Somer, 17 Lectures on Fermat Numbers, Springer-Verlag NY 2001, pp. 42-43.

Links

Dennis Martin, Table of n, a(n) for n = 0..11

Chris Caldwell, The Prime Pages: Pepin's Test.

Formula

a(n) = 3^((F(n) - 1)/2) (mod F(n)), where F(n) is the n-th Fermat Number

Example

a(4) = 3^(32768) (mod 65537) = 65536 = -1 (mod F(4)), therefore F(4) is prime.
a(5) = 3^(2147483648) (mod 4294967297) = 10324303 (mod F(5)), therefore F(5) is composite.

Crossrefs

Cf. A000215, A019434, A152154, A152155, A152156.

Sequence in context: A152921 A215116 A212297 * A144988 A067172 A013089

Adjacent sequences: A152150 A152151 A152152 * A152154 A152155 A152156

Keyword

nonn

Author

Dennis Martin (dennis.martin(AT)dptechnology.com), Nov 27 2008

Status

approved