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

Offset

1,1

Comments

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

Links

Table of n, a(n) for n=1..40.

Formula

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

Example

a(40) = 3 + 5 + 7 + 11 + 13 + 17 + 19 + 23 + 31 + 43 + 61 + 79 + 101 + 127 + 167 + 191 + 199 + 313 + 347 + 701 + 1709 + 2617 + 3539 + 5807 + 10501 + 10691 + 11279 + 12391 + 14479 + 42737 + 83339 + 95369 + 117239 + 127031 + 138937 + 141079 + 267017 + 269987 + 374321 + 986191.

Crossrefs

Cf. A000040, A000978.

Sequence in context: A159465 A071148 A172289 * A048598 A049717 A241565

Adjacent sequences: A172293 A172294 A172295 * A172297 A172298 A172299

Keyword

hard,nonn

Author

Jonathan Vos Post, Jan 30 2010

Status

approved