OFFSET
1,1
COMMENTS
Except the first term 4, all terms are odd since for even k, 2^k - 13 is divisible by 3.
LINKS
F. Firoozbakht and M. F. Hasler, Variations on Euclid's formula for Perfect Numbers, JIS 13 (2010) #10.3.1.
Henri Lifchitz and Renaud Lifchitz, Search for 2^n-13, PRP Top Records.
EXAMPLE
k = 5: 32 - 13 = 19 is prime.
MATHEMATICA
Select[Range[4, 20000], PrimeQ[2^#-13]&] (* Vladimir Joseph Stephan Orlovsky, Feb 27 2011 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Jul 13 2004
EXTENSIONS
a(16) from Max Alekseyev, a(17)-a(18) from Henri Lifchitz, a(19) from Lelio R Paula, added by Max Alekseyev, Feb 09 2012
a(20) found by Stefano Morozzi, added by Elmo R. Oliveira, Nov 17 2023
STATUS
approved