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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
Eric Weisstein's World of Mathematics, Thabit ibn Kurrah's rules
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 A344155 A344953
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 March 29 10:22 EDT 2024. Contains 371268 sequences. (Running on oeis4.)