A091880 - OEIS

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

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OFFSET

1,2

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

FORMULA

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

MATHEMATICA

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

CROSSREFS