A174267 Primes p such that 5^p - 4 is also prime.

5, 7, 47

Offset: 1

Author

Vincenzo Librandi, Mar 14 2010

Keywords

• nonn
• more
• bref

Comments

If it exists, a(4) > 48091. - J.W.L. (Jan) Eerland, Nov 13 2022

If it exists, a(4) > 2*10^5 (cf. comment by Tyler NeSmith in A059613). - Michael S. Branicky, Aug 17 2024

Examples

			For p=5, 5^5-4=3121; p=7, 5^7-4=78121; p=47, 5^47-4= 710542735760100185871124267578121
		

Crossrefs

Cf. A000040, A059613.

Programs

Magma

[p: p in PrimesUpTo(3500) | IsPrime(5^p-4)];

PARI

is(n)=isprime(n) && isprime(5^n-4) \\ Charles R Greathouse IV, Sep 06 2016

Formula

A000040 INTERSECT A059613. - R. J. Mathar, Apr 15 2010