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A091997 Numbers n such that 3*2^(n-1) - 1 is prime. 2
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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..49.

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

FORMULA

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

EXAMPLE

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

MATHEMATICA

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

PROG

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

CROSSREFS

Cf. A002235.

Sequence in context: A258085 A247350 A057484 * A124168 A309708 A285929

Adjacent sequences:  A091994 A091995 A091996 * A091998 A091999 A092000

KEYWORD

nonn

AUTHOR

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

EXTENSIONS

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

More terms from Jinyuan Wang, Jan 30 2020

STATUS

approved

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Last modified June 25 04:15 EDT 2021. Contains 345452 sequences. (Running on oeis4.)