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Search: id:A165779
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| A165779 |
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Numbers n such that |2^n-993| is prime. |
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+0
3
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| 1, 4, 6, 10, 14, 17, 26, 29, 54, 62, 77, 121, 344, 476, 1012, 1717, 1954, 2929, 2993, 3014, 3304, 4704
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OFFSET
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1,2
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COMMENT
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If p=2^n-993 is prime, then 2^(n-1)*p is a solution to sigma(x)-2x = 992 = 2^5*(2^5-1) = 2*A000396(3).
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EXAMPLE
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a(4)=10 since 2^10-993 = 31 is prime.
For exponents a(1)=1, a(2)=4 and a(3)=6, we get 2^a(k)-993 = -991, -977 and -929 which are negative, but which are prime in absolute value.
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CROSSREFS
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Cf. A096818, A165778, A165780.
Sequence in context: A123666 A095305 A058917 this_sequence A137860 A091376 A100484
Adjacent sequences: A165776 A165777 A165778 this_sequence A165780 A165781 A165782
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KEYWORD
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nonn
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AUTHOR
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M. F. Hasler (MHasler(AT)univ-ag.fr), Oct 11 2009
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