A036260 Numbers k > 1 such that k mod ord2(k) is even, where ord2(k) is the order of 2 mod k.

2921, 3017, 3473, 3479, 5767, 5969, 6167, 6377, 6497, 6913, 7223, 7519, 7567, 7751, 9017, 9271, 10199, 10447, 11431, 11929, 12719, 13439, 13609, 14513, 16583, 17009, 17143, 18631, 18809, 19313, 20737, 21119, 22337, 22351, 22537

Offset: 1

Author

David W. Wilson

Keywords

• nonn

Comments

These are all composite since for prime p, ord2(p) | phi(p) = p-1, whence p mod ord2(p) = 1.

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A002326, A007733, A036259.

Programs

Mathematica

Select[Range[3, 23000, 2], EvenQ[Mod[#, MultiplicativeOrder[2, #]]] &] (* Amiram Eldar, Jul 30 2020 *)

Extensions

Offset corrected by Amiram Eldar, Jul 30 2020