OFFSET
0,9
COMMENTS
It is conjectured that a(n) > 0 for all n > 52. See related conjecture and findings in A039669. Also see the graph of this sequence.
LINKS
Altug Alkan, Table of n, a(n) for n = 0..10000
EXAMPLE
a(7) = 0 because 2*7 + 1 - 2^1 = 13, 2*7 + 1 - 2^2 = 11, 2*7 + 1 - 2^3 = 7 are prime numbers.
PROG
(PARI) isA002808(n) = n>1 && !isprime(n);
a(n) = sum(k=1, log(2*n+1)\log(2), isA002808(2*n+1-2^k))
CROSSREFS
KEYWORD
nonn
AUTHOR
Altug Alkan, Feb 15 2017
STATUS
approved