A087370 Numbers n such that 3n - 1 is a prime.

1, 2, 4, 6, 8, 10, 14, 16, 18, 20, 24, 28, 30, 34, 36, 38, 44, 46, 50, 56, 58, 60, 64, 66, 76, 78, 80, 84, 86, 88, 90, 94, 98, 104, 106, 116, 118, 120, 128, 130, 134, 140, 144, 148, 150, 154, 156, 160, 164, 168, 170, 174, 186, 188, 190, 196, 198, 200, 206, 214, 216

Offset: 1

Author

Giovanni Teofilatto, Oct 21 2003

Keywords

• easy
• nonn

Comments

3*n - 1 is an Eisenstein prime. - Vincenzo Librandi, Aug 08 2010

For all elements of this sequence there are no pairs (x,y) of positive integers such that a(n) = 3*x*y - x + y. - Pedro Caceres, Jan 28 2021

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

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

A003627 gives primes, A091177 gives prime index.

Cf. A010051, subsequence of A016789, A259645.

Programs

Haskell

a087370 n = a087370_list !! (n-1)
a087370_list = filter ((== 1) . a010051' . subtract 1 . (* 3)) [0..]
-- Reinhard Zumkeller, Jul 03 2015

Formula

a(n)= A024893(n) + 1 = A088879(n) + 2.

Extensions

Corrected and extended by Ray Chandler, Oct 22 2003