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

2,1

Links

Table of n, a(n) for n=2..73.

Example

2^2-2 = 2 prime so a(1)=2, 3^2-2= 7 prime 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 A366441

Adjacent sequences: A147790 A147791 A147792 * A147794 A147795 A147796

Keyword

nonn

Author

Cino Hilliard, Nov 13 2008

Status

approved