A091178 Numbers k such that k-th prime is of the form 6*m+1.

4, 6, 8, 11, 12, 14, 18, 19, 21, 22, 25, 27, 29, 31, 34, 36, 37, 38, 42, 44, 46, 47, 48, 50, 53, 58, 59, 61, 63, 65, 67, 68, 70, 73, 74, 75, 78, 80, 82, 84, 85, 88, 90, 93, 95, 99, 100, 101, 105, 106, 110, 111, 112, 114, 115, 117, 121, 122, 125, 127, 129, 130

Offset: 1

Author

Ray Chandler, Dec 26 2003

Keywords

• nonn

Comments

A002476 indexed by A000040.

Also k for which prime(k) == 1 (mod 3). - Bruno Berselli, Mar 04 2016

Sequence A091177 (indices of primes of the form 3*k-1) is this sequence's complement in the positive integers without {2}. - M. F. Hasler, Sep 02 2016

The asymptotic density of this sequence is 1/2 (by Dirichlet's theorem). - Amiram Eldar, Feb 28 2021

Links

• Zak Seidov, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000040, A002476 (primes of the form 6*m+1), A091177 (indices of primes of the form 3*k-1), A024892, A024899.

Programs

Mathematica

Select[Range[200],IntegerQ[(Prime[#]-1)/6]&] (* Harvey P. Dale, Aug 25 2013 *)

PARI

isok(n) = !((prime(n)-1) % 6); \\ Michel Marcus, Mar 04 2016

Formula

a(n) = k such that A000040(k) = A002476(n).

Extensions

Definition edited by Zak Seidov, Oct 09 2014