A071428 Numbers n such that x^n + x^(n-1) + x^(n-2) + ... + x + 1 is irreducible over GF(3).

4, 6, 16, 18, 28, 30, 42, 52, 78, 88, 100, 112, 126, 136, 138, 148, 162, 172, 196, 198, 210, 222, 232, 256, 268, 280, 282, 292, 316, 330, 352, 378, 388, 400, 448, 460, 462, 486, 508, 520, 556, 568, 570, 592, 606, 616, 630, 640, 652, 676, 690, 700, 738, 750

Offset: 1

Author

Robert G. Wilson v, Jun 22 2002

Keywords

• easy
• nonn

Comments

n such that n+1 is a prime with primitive root 3 (A019334 except for the first term). [Joerg Arndt, Jul 05 2011]

Crossrefs

Cf. A071642.

Programs

PARI

for(n=2,1000,if(polisirreducible(Mod(1,3)*sum(e=0,n,x^e)),print1(n+1,", "))) /* Joerg Arndt, Jul 05 2011 */

PARI

forprime(p=5,1000,if(znorder(Mod(3,p))==p-1,print1(p-1,", "))) /* much faster */ /* Joerg Arndt, Jul 05 2011 */