A062574 Numbers k such that 8^k - 7^k is prime or a strong pseudoprime.

7, 11, 17, 29, 31, 79, 113, 131, 139, 4357, 44029, 76213, 83663, 173687, 336419, 615997

Offset: 1

Author

Mike Oakes, May 18 2001, May 19 2001

Keywords

• nonn
• hard

Comments

All terms are prime. - Alexander Adamchuk, Apr 27 2008

Links

• Henri & Renaud Lifchitz, PRP Records.

Crossrefs

Cf. A000043, A057468, A059801, A059802, A059803 (9^n-8^n is prime), A062572-A062666.

Cf. A016177 = 8^n - 7^n.

Programs

Mathematica

Select[Range[200], PrimeQ[8^# - 7^#] &] (* Vladimir Joseph Stephan Orlovsky, Feb 22 2012 *)

PARI

is(n)=ispseudoprime(8^n-7^n) \\ Charles R Greathouse IV, Sep 04 2013

Extensions

Two more terms 44029 and 76213 found by Ananda Tallur & Jean-Louis Charton in 2003.

Three more terms 83663, 173687 and 336419 found by Jean-Louis Charton in 2004 and 2008

New term 615997 found by Jean-Louis Charton corresponding to a probable prime with 556301 digits. Jean-Louis Charton, Sep 02 2009