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A087885 Numbers n such that 5^n + 2 is a prime. 13
0, 1, 3, 17, 143, 261, 551, 2285, 18731, 18995, 19751, 62067, 98051, 169727 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Terms <= 551 correspond to certified primes.

a(15) > 2*10^5. - Robert Price, Jan 16 2015

LINKS

Table of n, a(n) for n=1..14.

Henri & Renaud Lifchitz, PRP Records.

EXAMPLE

a(3)=3 is a member because 5^3 + 2 = 127 is a prime.

5^17 + 2 = 762939453127 is prime, hence 17 is a term.

MATHEMATICA

Do[If[PrimeQ[5^n + 2], Print[n]], {n, 1, 10000}] (* Ryan Propper, Jun 17 2005 *)

PROG

(PARI) for(n=0, 10^5, if(ispseudoprime(5^n+2), print1(n, ", "))) \\ Felix Fröhlich, Jun 04 2014

CROSSREFS

Cf. A051783 (3^n + 2 is prime).

Sequence in context: A120022 A001865 A189001 * A178685 A268254 A198860

Adjacent sequences:  A087882 A087883 A087884 * A087886 A087887 A087888

KEYWORD

hard,nonn

AUTHOR

Donald S. McDonald, Oct 13 2003

EXTENSIONS

{551, 2285} from Ryan Propper, Jun 17 2005

{18731, 18995, 19751, 62067} found by Mike Oakes in 2003. - Alexander Adamchuk, Mar 02 2008

Edited by Ray Chandler, Jul 27 2011

98051 from Ray Chandler, Jul 28 2011

a(14) from Robert Price, Jan 16 2015

STATUS

approved

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Last modified April 25 08:06 EDT 2018. Contains 303048 sequences. (Running on oeis4.)