A065507 Smallest prime q such that (p^q+1)/(p+1) is a prime, where p = prime(n).

3, 3, 5, 3, 5, 3, 7, 17, 11, 7, 109, 5, 17, 5, 5, 21943, 17, 7, 3, 5, 7, 3, 19, 13

Offset: 1

Author

Vladeta Jovovic, Nov 26 2001

Keywords

• hard
• more
• nonn

Comments

It is known that for the prime 97, a(25) > 31000. - T. D. Noe, Feb 13 2004

Links

• H. Dubner and T. Granlund, Primes of the Form (b^n+1)/(b+1), J. Integer Sequences, 3 (2000), #P00.2.7.

Crossrefs

Cf. A065854.

Cf. A084742 (least k such that (n^k+1)/(n+1) is prime).

Programs

Mathematica

Do[p = Prime[n]; k = 1; While[ !PrimeQ[ (p^Prime[k] + 1)/(p + 1)], k++ ]; Print[ Prime[k]], {n, 1, 15} ]

Extensions

More terms from T. D. Noe, Jan 22 2004