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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 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 FrÃ¶hlich, 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 December 9 21:30 EST 2018. Contains 318032 sequences. (Running on oeis4.)