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A087885
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Numbers k such that 5^k + 2 is a prime.
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13
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0, 1, 3, 17, 143, 261, 551, 2285, 18731, 18995, 19751, 62067, 98051, 169727, 442281
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OFFSET
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1,3
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COMMENTS
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Terms <= 551 correspond to certified primes.
a(15) > 2*10^5. - Robert Price, Jan 16 2015
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LINKS
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Table of n, a(n) for n=1..15.
Henri & Renaud Lifchitz, PRP Records.
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EXAMPLE
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a(3)=3 is a term because 5^3 + 2 = 127 is a prime.
5^17 + 2 = 762939453127 is prime, hence 17 is a term.
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MATHEMATICA
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Do[If[PrimeQ[5^n + 2], Print[n]], {n, 1, 10000}] (* Ryan Propper, Jun 17 2005 *)
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PROG
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(PARI) for(n=0, 10^5, if(ispseudoprime(5^n+2), print1(n, ", "))) \\ Felix Fröhlich, Jun 04 2014
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CROSSREFS
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Cf. A051783 (3^n + 2 is prime).
Sequence in context: A120022 A001865 A189001 * A178685 A268254 A333331
Adjacent sequences: A087882 A087883 A087884 * A087886 A087887 A087888
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KEYWORD
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hard,nonn
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AUTHOR
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Donald S. McDonald, Oct 13 2003
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EXTENSIONS
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a(7)-a(8) from Ryan Propper, Jun 17 2005
a(9)-a(12) found by Mike Oakes in 2003. - Alexander Adamchuk, Mar 02 2008
Edited by Ray Chandler, Jul 27 2011
a(13) from Ray Chandler, Jul 28 2011
a(14) from Robert Price, Jan 16 2015
a(15) from Paul Bourdelais, Jan 28 2021
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STATUS
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approved
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