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A128458 Numbers n such that 15^n - 2 is a prime. 13
1, 2, 3, 7, 12, 17, 19, 51, 65, 550, 1460, 1641, 7035, 18002, 20963, 21163, 42563, 94906, 148048 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

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

LINKS

Table of n, a(n) for n=1..19.

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 *)

CROSSREFS

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.

Sequence in context: A168249 A080140 A019568 * A066733 A049623 A302506

Adjacent sequences:  A128455 A128456 A128457 * A128459 A128460 A128461

KEYWORD

hard,more,nonn

AUTHOR

Alexander Adamchuk, Mar 14 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

STATUS

approved

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Last modified January 24 01:05 EST 2020. Contains 331178 sequences. (Running on oeis4.)