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Search: id:A099481
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| A099481 |
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Numbers n such that 2^n-n^2 is a semiprime. |
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+0
3
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| 11, 13, 15, 21, 23, 37, 39, 41, 43, 47, 49, 55, 67, 75, 103, 105, 133, 147, 153, 161, 163, 177, 201, 209, 221, 239, 249, 263, 311, 335, 355, 397, 413, 421, 437, 447
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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The smaller prime factor of the 125-digit semiprime 2^413-413^2 has 40 digits, for the 127-digit semiprime 2^421-421^2 the smaller prime factor has 45 digits. The next term is >= 583. - Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 14 2007
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LINKS
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Dario Alpern, Factorization using the Elliptic Curve Method.
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EXAMPLE
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a(1)=11 because 2^11-11^2=1927=41*47.
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CROSSREFS
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Cf. A024012 2^n-n^2, A099482 semiprimes of the form 2^n-n^2, A072180 2^n-n^2 is prime, A075896 primes of the form 2^n-n^2.
Sequence in context: A152200 A124569 A049722 this_sequence A068569 A124176 A031979
Adjacent sequences: A099478 A099479 A099480 this_sequence A099482 A099483 A099484
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KEYWORD
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hard,nonn
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AUTHOR
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Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 18 2004
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EXTENSIONS
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More terms from Hugo Pfoertner (hugo(AT)pfoertner.org), Oct 14 2007
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