A165681 Primes p such that 3*p*(p-1)+1 is not prime.

13, 17, 19, 23, 37, 41, 47, 61, 71, 73, 79, 83, 97, 101, 103, 107, 113, 127, 131, 139, 149, 151, 163, 167, 179, 181, 191, 193, 199, 211, 223, 227, 229, 233, 241, 251, 257, 263, 269, 271, 277, 281, 283, 293, 307, 311, 317, 331, 337, 349, 359, 367, 373, 379, 383, 397, 401

Offset: 1

Author

Vincenzo Librandi, Sep 24 2009

Keywords

• nonn
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A165682, A165683.

Programs

Mathematica

Select[Prime[Range[90]],!PrimeQ[3#(#-1)+1]&]  (* Harvey P. Dale, Mar 18 2011 *)

PARI

is(n)=isprime(n) && !isprime(3*n*(n-1)+1) \\ Charles R Greathouse IV, Feb 23 2017

Formula

A000040 \ A165682.

a(n) ~ n log n. - Charles R Greathouse IV, Feb 23 2017

Extensions

2 and 3 removed by R. J. Mathar, Sep 26 2009