A147793 Smallest prime q such that p^q-2 is prime where p ranges over the set of prime numbers.

2, 2, 2, 2, 2, 2, 2, 3, 2, 2, 2, 2, 3, 2, 2, 2, 2, 3, 2, 2, 2, 3, 149, 2, 5, 2, 7, 2, 2, 5, 2, 2, 3, 2, 5, 3, 89, 2, 2, 2, 13, 2, 3, 367, 2, 17, 3, 2, 2, 3, 2, 2, 2, 2, 439, 2, 61, 127, 2, 2, 3, 2, 37, 2, 3, 2, 2, 2, 2, 2, 2, 2

Offset

1,1

Links

Table of n, a(n) for n=1..72.

Example

2^2-2 = 2 prime, so a(1)=2.
3^2-2 = 7 prime, so a(2)=2.
For q=2,3,5, 199^q-2 is not prime.
For q=7, 199^7-2 = 12358664279161397 prime so a(27)=7.

Prog

(PARI) g2(n) = forprime(x=2, n, y=g(1000, x); if(y>0, print1(y", ")))
g(n, m) = p1=0; forprime(p=2, n, y=m^p-2; if(ispseudoprime(y), p1=p; break)); p1

Crossrefs

Sequence in context: A001991 A305706 A359309 * A352201 A052298 A388258

Adjacent sequences: A147790 A147791 A147792 * A147794 A147795 A147796

Keyword

nonn

Author

Cino Hilliard, Nov 13 2008

Extensions

Offset 1 from Michel Marcus, May 07 2025

Status

approved