A065507 - OEIS

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

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OFFSET

1,1

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.

MATHEMATICA

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

CROSSREFS

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

KEYWORD

hard,more,nonn

AUTHOR

EXTENSIONS

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

STATUS

approved