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

1, 2, 3, 7, 12, 17, 19, 51, 65, 550, 1460, 1641, 7035, 18002, 20963, 21163, 42563, 94906, 148048

Offset: 1

Author

Alexander Adamchuk, Mar 14 2007

Keywords

• nonn
• hard
• more

Comments

a(20) > 2*10^5. - Robert Price, Jun 23 2015

Crossrefs

Cf. A084714 (smallest prime of the form (2n-1)^k - 2).

Cf. A128472 (smallest prime of the form (2n-1)^k - 2 for k > (2n-1)).

Cf. A014224, A109080, A090669, A128455, A128457, A128459, A128460, A128461.

Programs

Mathematica

Do[ f = 15^n - 2; If[ PrimeQ[ f ], Print[ {n, f} ] ], {n,1,1000} ]
Do[If[PrimeQ[15^n - 2], Print[n]], {n, 10^4}] (* Ryan Propper, Jun 06 2007 *)

Extensions

550 from Stefan Steinerberger, May 05 2007

3 more terms from Ryan Propper, Jun 06 2007

a(14)-a(19) from Robert Price, Jun 23 2015