3,2

a(2) = 131072, or it is a Sierpiński number multiplied by a power of 2.

Because a(1) = 8 but a(2) is unknown, we do not include it here; we set the offset to 3.

a(2) <= 201446503145165177.

Table of n, a(n) for n=3..11.

Dan Krywaruczenko, A Reverse Sierpiński Number Problem

Cf. A123159.

Sequence in context: A013800 A013870 A195898 * A164526 A278897 A123652

Adjacent sequences: A263497 A263498 A263499 * A263501 A263502 A263503

nonn,more,hard

Arkadiusz Wesolowski, Oct 19 2015

approved