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 A124621 Numbers k such that 5^k + 4 is prime. 7
 0, 2, 6, 10, 102, 494, 794, 1326, 5242, 5446, 24602, 87606, 188558 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS a(13) > 10^5. - Robert Price, Feb 03 2014 a(14) > 2*10^5. - Tyler NeSmith, May 04 2021 LINKS F. Firoozbakht, M. F. Hasler, Variations on Euclid's formula for Perfect Numbers, JIS 13 (2010) #10.3.1 EXAMPLE 5^2 + 4 = 29 is prime, so 2 is a term. MATHEMATICA Select[Range[0, 2000], PrimeQ[5^# + 4] &] (* Vincenzo Librandi, Oct 01 2012 *) PROG (PARI) is(n)=ispseudoprime(5^n+4) \\ Charles R Greathouse IV, Feb 17 2017 CROSSREFS Cf. A059613. Sequence in context: A322756 A048782 A083458 * A325237 A065799 A162582 Adjacent sequences:  A124618 A124619 A124620 * A124622 A124623 A124624 KEYWORD nonn AUTHOR Artur Jasinski, Dec 21 2006 EXTENSIONS Added the first term 0 by Vincenzo Librandi, Oct 01 2012 a(9) - a(10) from Bruno Berselli, Aug 12 2013 a(11)-a(12) from Robert Price, Feb 03 2014 a(13) from Tyler NeSmith, May 04 2021 STATUS approved

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Last modified June 14 12:26 EDT 2021. Contains 345025 sequences. (Running on oeis4.)