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A092561
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"Mersenne" semiprimes, semiprimes of the form 2^n-1.
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6
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1, 15, 511, 2047, 8388607, 137438953471, 2199023255551, 562949953421311, 576460752303423487, 147573952589676412927, 9671406556917033397649407, 158456325028528675187087900671, 2535301200456458802993406410751
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| 2047 is a member because 2047 = 2^11-1 = 23*89
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MATHEMATICA
| a := Select[Range[120], ! PrimeQ[2^# - 1] && Length[Divisors[2^# - 1]] <= 4 &]; 2^a - 1 - Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Apr 12 2006
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CROSSREFS
| Corresponding n: A085724.
Cf. A092558, A092559 and A092562.
Sequence in context: A203525 A004703 A203326 * A009068 A157166 A074040
Adjacent sequences: A092558 A092559 A092560 * A092562 A092563 A092564
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KEYWORD
| nonn
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AUTHOR
| Zak Seidov (zakseidov(AT)yahoo.com), Feb 27 2004
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EXTENSIONS
| One more term from Stefan Steinerberger (stefan.steinerberger(AT)gmail.com), Apr 12 2006
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