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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 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 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

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Last modified June 19 12:57 EDT 2021. Contains 345129 sequences. (Running on oeis4.)