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