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 term 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
KEYWORD
hard,nonn
AUTHOR
Donald S. McDonald, Oct 13 2003
EXTENSIONS
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
STATUS
approved