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Search: id:A039772
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| A039772 |
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phi(a(n)) and (a(n)-1) have a common factor, are distinct and a(n) is even. |
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+0
2
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| 28, 52, 66, 70, 76, 112, 124, 130, 148, 154, 172, 176, 186, 190, 196, 208, 232, 238, 244, 246, 268, 276, 280, 286, 292, 304, 310, 316, 322, 344, 364, 366, 370, 388, 396, 406, 412, 418, 426, 430, 436, 442, 448, 490, 496, 506, 508, 520, 532, 556, 568, 574
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Also a(n) is the union of all possible even Fermat pseudoprimes q to some prime base p>q such that q does not divide p-1. Note that all even nonprime divisors of p-1 are the Fermat pseudoprimes to prime base p. E.g. q = {4,6,12,18,28,36} is a set of even Fermat pseudoprimes to prime base p = 37, but only number q = 28 from this set does not divide p-1 = 36. - Alexander Adamchuk (alex(AT)kolmogorov.com), Jun 16 2007
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LINKS
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Eric Weisstein, Link to a section of The World of Mathematics. Fermat Pseudoprime.
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EXAMPLE
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phi(28)=12, gcd(12,27)=3.
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CROSSREFS
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Cf. A000010.
Sequence in context: A039615 A046419 A063770 this_sequence A043134 A039311 A043914
Adjacent sequences: A039769 A039770 A039771 this_sequence A039773 A039774 A039775
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KEYWORD
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nonn,easy
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AUTHOR
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Olivier Gerard (ogerard(AT)ext.jussieu.fr)
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