A015921 - OEIS

A015921

Positive integers n such that 2^n == 4 (mod n).

1, 2, 4, 6, 10, 12, 14, 22, 26, 30, 34, 38, 46, 58, 62, 74, 82, 86, 94, 106, 118, 122, 132, 134, 142, 146, 158, 166, 170, 178, 182, 194, 202, 206, 214, 218, 226, 254, 262, 274, 278, 298, 302, 314, 326, 334, 346, 358, 362, 372, 382, 386, 394, 398, 422, 446

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OFFSET

1,2

COMMENTS

Odd terms are given by A173572.

For all m, 2^A050259(m)-1 belongs to this sequence.

LINKS

T. D. Noe, Table of n, a(n) for n = 1..1000

OEIS Wiki, 2^n mod n

MATHEMATICA

Select[Range[500], PowerMod[2, #, #] == 4 &] (* Alonso del Arte, Jul 07 2011 *)

CROSSREFS