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Search: id:A091996
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| A091996 |
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Numbers n such that 9*2^(2*n-1) - 1 is prime. |
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+0
1
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| 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; listen)
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OFFSET
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1,2
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LINKS
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Eric Weisstein's World of Mathematics, Thabit ibn Kurrah's rules
Kosmaj, Riesel list k<300.
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EXAMPLE
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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
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PROGRAM
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(PARI) for (i=1, 500, if(isprime(9*2^(2*i-1)-1), print1(i, ", ")))
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CROSSREFS
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Sequence in context: A118248 A132679 A116617 this_sequence A085262 A060406 A001839
Adjacent sequences: A091993 A091994 A091995 this_sequence A091997 A091998 A091999
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KEYWORD
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nonn
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AUTHOR
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Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 17 2004
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EXTENSIONS
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8 additional terms, corresponding to pseudoprimes, from Ryan Propper (rpropper(AT)stanford.edu), Jun 18 2005
More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Apr 28 2007
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