A091880 A049232 indexed by A000040.

1, 4, 9, 14, 15, 18, 21, 22, 25, 36, 39, 40, 48, 53, 59, 65, 67, 70, 72, 73, 74, 82, 85, 88, 99, 101, 110, 114, 122, 125, 127, 129, 130, 137, 143, 146, 147, 155, 158, 168, 174, 177, 180, 181, 188, 194, 198, 200, 202, 204, 213, 216, 219, 220, 224, 226, 229, 235

Offset: 1

Author

Ray Chandler, Feb 15 2004

Keywords

• easy
• nonn

Comments

The asymptotic density of this sequence is 1 - 2 * Product_{p prime} (1-1/(p*(p-1))) = 1 - 2 * A005596 = 0.252088... - Amiram Eldar, Feb 28 2021

Links

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

Crossrefs

Cf. A000040, A005596, A049232.

Programs

Mathematica

Select[Range[100], ! SquareFreeQ[Prime[ # ] + 2] &] (* Zak Seidov, Oct 28 2008 *)

Formula

a(n) = k such that A000040(k) = A049232(n).