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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..31.

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

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

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

STATUS

approved

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Last modified November 15 21:33 EST 2019. Contains 329155 sequences. (Running on oeis4.)