A091997 Numbers n such that 3*2^(n-1) - 1 is prime.

1, 2, 3, 4, 5, 7, 8, 12, 19, 35, 39, 44, 56, 65, 77, 95, 104, 144, 207, 217, 307, 325, 392, 459, 471, 828, 1275, 3277, 4205, 5135, 7560, 12677, 14899, 18124, 18820, 25691, 26460, 41629, 51388, 71784, 80331, 85688, 88172, 97064, 123631, 155931, 164988, 234761, 414841

Offset: 1

Author

Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 17 2004

Keywords

• nonn

Examples

			3*2^(3-1) - 1 = 11 so a(1) = 3.
		

Links

• Eric Weisstein's World of Mathematics, Thabit ibn Kurrah's rules

Crossrefs

Cf. A002235.

Programs

Mathematica

Do[If[PrimeQ[3*2^(n - 1) - 1], Print[n]], {n, 1, 8000}] (* Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006 *)

PARI

for (i=1,1000,if(isprime(3*2^(i-1)-1),print1(i,",")))

Formula

a(n) = A002235(n) + 1. - Jinyuan Wang, Jan 30 2020

Extensions

More terms from Mohammed Bouayoun (Mohammed.Bouayoun(AT)yahoo.fr), Apr 13 2006

More terms from Jinyuan Wang, Jan 30 2020