A069254 k/10 when gcd(k, 2^k+1) = 5.

1, 3, 7, 9, 11, 13, 17, 19, 21, 23, 27, 29, 31, 33, 37, 43, 47, 49, 51, 53, 57, 59, 61, 63, 67, 69, 71, 73, 77, 79, 81, 83, 87, 89, 91, 93, 97, 99, 101, 103, 107, 109, 111, 113, 119, 121, 127, 129, 131, 133, 137, 139, 141, 143, 147, 149, 151, 153, 157, 159, 161, 163

Offset: 1

Author

Benoit Cloitre, Apr 13 2002

Keywords

• easy
• nonn

Comments

The number of terms not exceeding 10^m, for m = 1, 2, ..., are 4, 38, 371, 3726, 37259, 372542, 3725411, 37254006, 372539990, ... . Apparently, the asymptotic density of this sequence exists and equals 0.3725... . - Amiram Eldar, Jun 14 2022

Links

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

Crossrefs

Cf. A069226.

Programs

Mathematica

Select[Range[170], GCD[10*#, PowerMod[2, 10*#, 10*#] + 1] == 5 &] (* Amiram Eldar, Jun 14 2022*)

PARI

lista(nn) = select(x->(gcd(x, 2^x+1) == 5), [1..nn])/10 \\ Michel Marcus, Oct 27 2019