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 A128458 Numbers n such that 15^n - 2 is a prime. 13

%I

%S 1,2,3,7,12,17,19,51,65,550,1460,1641,7035,18002,20963,21163,42563,

%T 94906,148048

%N Numbers n such that 15^n - 2 is a prime.

%C a(20) > 2*10^5. - _Robert Price_, Jun 23 2015

%t Do[ f = 15^n - 2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n,1,1000} ]

%t Do[If[PrimeQ[15^n - 2], Print[n]], {n, 10^4}] (* _Ryan Propper_, Jun 06 2007 *)

%Y Cf. A084714 = smallest prime of the form (2n-1)^k - 2, or 0 if no such number exists. Cf. A128472 = smallest prime of the form (2n-1)^k - 2 for k>(2n-1), or 0 if no such number exists. Cf. A014224, A109080, A090669, A128455, A128457, A128459, A128460, A128461.

%K hard,more,nonn

%O 1,2

%A _Alexander Adamchuk_, Mar 14 2007

%E 550 from _Stefan Steinerberger_, May 05 2007

%E 3 more terms from _Ryan Propper_, Jun 06 2007

%E a(14)-a(19) from _Robert Price_, Jun 23 2015

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Last modified May 16 08:07 EDT 2021. Contains 343940 sequences. (Running on oeis4.)