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A099441
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Numbers n such that A000295(n) = 2^n-n-1 is a semiprime.
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3
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3, 5, 6, 8, 9, 12, 30, 32, 33, 46, 52, 62, 74, 76, 86, 98, 130, 134, 154, 228, 230, 242, 256, 266, 346, 352, 382, 412, 428, 474, 488
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OFFSET
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1,1
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COMMENTS
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A candidate for the next term is a(32) = 634. 2^634-635 is composite with 191 decimal digits and unknown factorization. - Hugo Pfoertner, Aug 13 2007
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LINKS
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EXAMPLE
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a(3) = 6 because 2^6-6-1 = 57 = 3*19 is a semiprime.
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CROSSREFS
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KEYWORD
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hard,more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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