

A124621


Numbers k such that 5^k + 4 is prime.


7



0, 2, 6, 10, 102, 494, 794, 1326, 5242, 5446, 24602, 87606, 188558
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OFFSET

1,2


COMMENTS

a(13) > 10^5.  Robert Price, Feb 03 2014
a(14) > 2*10^5.  Tyler NeSmith, May 04 2021


LINKS

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


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



