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Smallest prime q such that (p^q+1)/(p+1) is a prime, where p = prime(n).
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%I #12 Oct 30 2017 04:32:23

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

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

%C It is known that for the prime 97, a(25) > 31000. - _T. D. Noe_, Feb 13 2004

%H H. Dubner and T. Granlund, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL3/DUBNER/dubner.html">Primes of the Form (b^n+1)/(b+1)</a>, J. Integer Sequences, 3 (2000), #P00.2.7.

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

%Y Cf. A065854.

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

%K hard,more,nonn

%O 1,1

%A _Vladeta Jovovic_, Nov 26 2001

%E More terms from _T. D. Noe_, Jan 22 2004