A176176 Numbers k such that 2^(k-1) == 4^(k-1) (mod k).

1, 2, 3, 4, 5, 7, 8, 11, 13, 16, 17, 19, 23, 28, 29, 31, 32, 37, 41, 43, 47, 53, 59, 61, 64, 67, 71, 73, 79, 83, 89, 97, 101, 103, 107, 109, 112, 113, 127, 128, 131, 137, 139, 149, 151, 157, 163, 167

Offset

1,2

Comments

Numbers k such that A062173(k) = A062175(k).

Question: is the sequence (Powers of 2) UNION (odd primes), the union of A000079 and A005408?

The answer to the question is no: 2^(28-1) mod 28 = 4^(28-1) mod 28 = 8. Also, any base-2 Fermat pseudoprime (A001567) is a term of this sequence. - D. S. McNeil, Dec 07 2010

Links

Harvey P. Dale, Table of n, a(n) for n = 1..10000

Mathematica

Select[Range[200], PowerMod[2, #-1, #]==PowerMod[4, #-1, #]&] (* Harvey P. Dale, Nov 10 2011 *)

Crossrefs

Cf. A000079, A005408, A062173.

Sequence in context: A348284 A162721 A378441 * A174090 A280083 A020902

Adjacent sequences: A176173 A176174 A176175 * A176177 A176178 A176179

Keyword

nonn

Author

Juri-Stepan Gerasimov, Dec 07 2010

Extensions

Extended by D. S. McNeil, Dec 07 2010

Status

approved