A172296 Partial sums of Wagstaff numbers A000978.

3, 8, 15, 26, 39, 56, 75, 98, 129, 172, 233, 312, 413, 540, 707, 898, 1097, 1410, 1757, 2458, 4167, 6784, 10323, 16130, 26631, 37322, 48601, 60992, 75471, 118208, 201547, 296916, 414155, 541186, 680123, 821202, 1088219, 1358206, 1732527, 2718718, 6750117

Offset: 1

Author

Jonathan Vos Post, Jan 30 2010

Keywords

• hard
• nonn

Comments

The prime partial sums of Wagstaff numbers begin 3, 233, 1097, 201547, 680123. None of these but 3 is itself a Wagstaff number.

Examples

			a(4) = 3 + 5 + 7 + 11 = 26.
		

Crossrefs

Cf. A000040, A000978.

Formula

a(n) = Sum_{i=1..n} {integers i such that (2^i + 1)/3 is prime}.

Extensions

a(41) added from the data at A000978 by Amiram Eldar, Jul 22 2025