A069171 Numbers k such that gcd(k, 2^k-1) = 3.

6, 12, 24, 30, 48, 66, 78, 96, 102, 114, 132, 138, 150, 174, 186, 192, 204, 222, 228, 246, 258, 264, 276, 282, 318, 348, 354, 366, 372, 384, 390, 402, 426, 438, 444, 456, 474, 492, 498, 510, 516, 528, 534, 552, 564, 570, 582, 606, 618, 636, 642, 654, 678

Offset: 1

Author

Benoit Cloitre, Apr 09 2002

Keywords

• easy
• nonn

Comments

The number of terms not exceeding 10^m, for m = 1, 2, ..., are 1, 8, 79, 793, 7935, 79349, 793524, 7935094, 79350930, 793509394, ... . Apparently, the asymptotic density of this sequence exists and equals 0.0793509... . - Amiram Eldar, Jun 14 2022

Links

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

Crossrefs

Cf. A014491.

Programs

Mathematica

Select[Range[700],GCD[#,2^#-1]==3&] (* Harvey P. Dale, Nov 22 2011 *)
Select[Range[700], GCD[#, PowerMod[2, #, #] - 1] == 3 &] (* Amiram Eldar, Jun 14 2022 *)