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%I #22 May 04 2021 20:04:39
%S 0,2,6,10,102,494,794,1326,5242,5446,24602,87606,188558
%N Numbers k such that 5^k + 4 is prime.
%C a(13) > 10^5. - _Robert Price_, Feb 03 2014
%C a(14) > 2*10^5. - _Tyler NeSmith_, May 04 2021
%H F. Firoozbakht, M. F. Hasler, <a href="https://cs.uwaterloo.ca/journals/JIS/VOL13/Hasler/hasler2.html">Variations on Euclid's formula for Perfect Numbers</a>, JIS 13 (2010) #10.3.1
%e 5^2 + 4 = 29 is prime, so 2 is a term.
%t Select[Range[0, 2000], PrimeQ[5^# + 4] &] (* _Vincenzo Librandi_, Oct 01 2012 *)
%o (PARI) is(n)=ispseudoprime(5^n+4) \\ _Charles R Greathouse IV_, Feb 17 2017
%Y Cf. A059613.
%K nonn
%O 1,2
%A _Artur Jasinski_, Dec 21 2006
%E Added the first term 0 by _Vincenzo Librandi_, Oct 01 2012
%E a(9) - a(10) from _Bruno Berselli_, Aug 12 2013
%E a(11)-a(12) from _Robert Price_, Feb 03 2014
%E a(13) from _Tyler NeSmith_, May 04 2021
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