A055685 Numbers k such that 2^k == -1 (mod k-1).

2, 6, 66, 378, 1190, 1470, 25806, 58590, 134946, 137346, 170586, 272610, 285390, 420210, 538734, 592410, 618450, 680706, 778806, 1163066, 1520442, 1700946, 2099202, 2831010, 4020030, 4174170, 4516110, 5059890, 5215770

Offset

1,1

Comments

The sequence is infinite. In fact, even its intersection with A006517 (given by A219037) is infinite.

Links

Chai Wah Wu, Table of n, a(n) for n = 1..1192

Kin Y. Li et al., Solution to Problem 323, Mathematical Excalibur 14(2), 2009, p. 3.

Formula

a(n) = A296369(n) + 1.

Mathematica

Do[If[PowerMod[2, n, n-1]==n-2, Print[n]], {n, 2, 12900000}]

Prog

(Python)
A055685_list = [n for n in range(2, 10**6) if pow(2, n, n-1) == n-2] # Chai Wah Wu, Nov 04 2019

Crossrefs

Cf. A064935, A006517, A219037, A296369.

Sequence in context: A061999 A066756 A070872 * A368511 A368512 A262047

Adjacent sequences: A055682 A055683 A055684 * A055686 A055687 A055688

Keyword

nonn

Author

Robert G. Wilson v, Jun 09 2000

Extensions

Edited by Max Alekseyev, Oct 11 2012

Incorrect term 4285390 removed by Chai Wah Wu, Nov 04 2019

Status

approved