0,9

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.

Altug Alkan, Table of n, a(n) for n = 0..10000

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.

(PARI) isA002808(n) = n>1 && !isprime(n);

a(n) = sum(k=1, log(2*n+1)\log(2), isA002808(2*n+1-2^k))

Cf. A002808, A039669, A067526, A109925.

Sequence in context: A035204 A326987 A190775 * A016154 A307332 A275409

Adjacent sequences: A282456 A282457 A282458 * A282460 A282461 A282462

nonn

Altug Alkan, Feb 15 2017

approved