

A091996


Numbers n such that 9*2^(2*n1)  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
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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*11)  1 = 17 so a(1)=1
9*2^(2*21)  1 = 71 so a(2)=2
9*2^(2*31)  1 = 287 is not prime
9*2^(2*41)  1 = 1151 is prime so a(3)=4


PROG

(PARI) for (i=1, 500, if(isprime(9*2^(2*i1)1), print1(i, ", ")))


CROSSREFS

Sequence in context: A132679 A216576 A116617 * A085262 A344155 A233273
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



