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A091996 Numbers n such that 9*2^(2*n-1) - 1 is prime. 0
1, 2, 4, 7, 8, 11, 22, 32, 50, 55, 80, 106, 155, 172, 208, 235, 391, 436, 470, 776, 1558, 1675, 2795, 2908, 2947, 3970, 4004, 5774, 6248, 11278, 11824, 17824, 41708, 51530, 92500, 137930, 192122, 242488, 251947, 414355 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

LINKS

Table of n, a(n) for n=1..40.

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

Kosmaj, Riesel list k<300.

EXAMPLE

9*2^(2*1-1) - 1 = 17 so a(1)=1

9*2^(2*2-1) - 1 = 71 so a(2)=2

9*2^(2*3-1) - 1 = 287 is not prime

9*2^(2*4-1) - 1 = 1151 is prime so a(3)=4

PROG

(PARI) for (i=1, 500, if(isprime(9*2^(2*i-1)-1), print1(i, ", ")))

CROSSREFS

Sequence in context: A132679 A216576 A116617 * A085262 A233273 A270200

Adjacent sequences:  A091993 A091994 A091995 * A091997 A091998 A091999

KEYWORD

nonn

AUTHOR

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

EXTENSIONS

8 additional terms, corresponding to probable primes, from Ryan Propper, Jun 18 2005

More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007

Edited by T. D. Noe, Oct 30 2008

STATUS

approved

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Last modified November 21 15:00 EST 2019. Contains 329371 sequences. (Running on oeis4.)