A089681 Numbers n such that 3n^2 - 1 is prime.

1, 2, 4, 6, 8, 12, 14, 18, 22, 26, 28, 30, 34, 40, 44, 48, 50, 52, 54, 58, 60, 70, 72, 74, 76, 78, 92, 96, 110, 118, 122, 136, 138, 144, 150, 154, 158, 164, 176, 182, 186, 188, 204, 210, 214, 216, 230, 232, 234, 236, 242, 248, 260, 268, 272, 274, 280, 298, 304, 308

Offset: 1

Author

Giovanni Teofilatto, Jan 05 2004

Keywords

• easy
• nonn

References

• M. Cerasoli, F. Eugeni and M. Protasi, Elementi di Matematica Discreta, Bologna 1988
• Emanuele Munarini and Norma Zagaglia Salvi, Matematica Discreta,UTET, CittaStudiEdizioni, Milano 1997

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000

Programs

Mathematica

Select[Range[500],PrimeQ[3#^2-1]&] (* Harvey P. Dale, Oct 09 2011 *)

PARI

is(n)=isprime(3*n^2-1) \\ Charles R Greathouse IV, Jun 05 2017

Extensions

More terms from Rick L. Shepherd, May 18 2005