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Search: id:A138921
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| A138921 |
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Indices k such that A020508(k)=Phi[k](-9) is prime, where Phi is a cyclotomic polynomial. |
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1
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| 3, 9, 12, 15, 20, 27, 33, 36, 59, 69, 91, 152, 207, 223, 232, 264, 336, 340, 380, 381, 492, 533, 540, 547, 549, 585, 615, 624, 627, 720, 773
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Most terms of this sequence are multiples of 3, exceptions are 20, 59, 91, 152, 223, 232, 340, 380, 533, 547, 773... corresponding to a(n) with n=5, 9, 11, 12, 14, 15, 18, 19, 22, 24, 31...
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LINKS
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Yves Gallot, Cyclotomic polynomials and prime numbers
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PROGRAM
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(PARI) for( i=1, 999, ispseudoprime( polcyclo(i, -9)) & print1( i", ")) /* use ...subst(polcyclo(i), x, -9)... in PARI < 2.4.2 */
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CROSSREFS
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Cf. A020508, A138920-A138940.
Sequence in context: A073536 A077468 A089425 this_sequence A136290 A103531 A108860
Adjacent sequences: A138918 A138919 A138920 this_sequence A138922 A138923 A138924
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KEYWORD
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nonn,more
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AUTHOR
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M. F. Hasler (www.univ-ag.fr/~mhasler), Apr 03 2008
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