OFFSET
1,1
COMMENTS
Conjecture: 6 is the only term whose prime factorization contains a single 2.
The largest odd divisor of each term is prime, that is, subsequence of A038550. - J. Lowell, Apr 13 2018
This sequence contains only certain terms from A092559 and certain multiples of 32. - Jon E. Schoenfield, Apr 18 2018 [with thanks to J. Lowell]
EXAMPLE
12 is a term because (2^12 + 1)/17 = 241, a prime number.
PROG
(Sage)
def a(n):
num = 2^n + 1
k = 0
while k < log(n, 2):
if num % (2^(2^k) + 1) == 0 and is_prime(Integer(num/(2^(2^k)+1))):
return True
k = k + 1
return False # Ralf Stephan, May 15 2014
CROSSREFS
KEYWORD
nonn,more
AUTHOR
J. Lowell, May 03 2014
EXTENSIONS
More terms from Ralf Stephan, May 15 2014
a(40)-a(46) from Jon E. Schoenfield, Apr 14 2018
Wrong property removed by J. Lowell, Apr 14 2018
STATUS
approved