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A065507 Smallest prime q such that (p^q+1)/(p+1) is a prime, where p = prime(n). 19
3, 3, 5, 3, 5, 3, 7, 17, 11, 7, 109, 5, 17, 5, 5, 21943, 17, 7, 3, 5, 7, 3, 19, 13 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

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

LINKS

Table of n, a(n) for n=1..24.

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. A065854.

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

Sequence in context: A073081 A094928 A178984 * A182731 A267518 A101772

Adjacent sequences:  A065504 A065505 A065506 * A065508 A065509 A065510

KEYWORD

hard,more,nonn

AUTHOR

Vladeta Jovovic, Nov 26 2001

EXTENSIONS

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

STATUS

approved

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Last modified October 15 20:04 EDT 2019. Contains 328037 sequences. (Running on oeis4.)