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