OFFSET
1,1
COMMENTS
Similar to A057202 (which allows negative primes): this sequence is obtained by dropping the first four terms of A057202. - Joerg Arndt, Oct 05 2012
LINKS
Henri Lifchitz and Renaud Lifchitz, Search for 2^n-21, PRP Top Records.
EXAMPLE
k = 5: 32 - 21 = 11 is prime.
k = 7: 128 - 21 = 107 is prime.
MATHEMATICA
Select[Range[5, 20000], PrimeQ[2^#-21]&] (* Vladimir Joseph Stephan Orlovsky, Feb 27 2011 *)
PROG
(Sage)
def is_A096820(n):
t = 2^n-21
return t > 1 and is_prime(t)
def A096820_list(up_to):
return [n for n in range(up_to) if is_A096820(n)]
A096820_list(100) # Peter Luschny, Oct 04 2012
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Labos Elemer, Jul 13 2004
EXTENSIONS
a(23)-a(24) from Max Alekseyev, a(25) from Donovan Johnson, a(26)-a(28) from Henri Lifchitz, a(29)-a(30) from Lelio R Paula, added by Max Alekseyev, Feb 10 2012
a(31)-a(32) from Lelio R Paula, added by Max Alekseyev, Oct 24 2013
a(33)-a(34) found by Lelio R Paula, a(35)-a(38) found by Stefano Morozzi, added by Elmo R. Oliveira, Nov 24 2023
STATUS
approved