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

Author

Juri-Stepan Gerasimov, Dec 07 2010

Keywords

• nonn

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

Crossrefs

Cf. A000079, A005408, A062173.

Programs

Mathematica

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

Extensions

Extended by D. S. McNeil, Dec 07 2010