A124621 Numbers k such that 5^k + 4 is prime.

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

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: A048782 A358739 A083458 * A325237 A358071 A065799

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