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Search: id:A138929
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| 2, 4, 6, 8, 10, 14, 16, 18, 22, 26, 32, 34, 38, 46, 50, 54, 58, 62, 64, 74, 82, 86, 94, 98, 106, 118, 122, 128, 134, 142, 146, 158, 162, 166, 178, 194, 202, 206, 214, 218, 226, 242, 250, 254, 256, 262, 274, 278, 298, 302, 314, 326, 334, 338, 346, 358, 362, 382
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Except for the initial term a(1)=2, indices k such that A020513(k)=Phi[k](-1) is prime, where Phi is a cyclotomic polynomial.
This is illustrated by the PARI code, although it is probably more efficient to calculate a(n) as 2*A000961(n).
{ a(n)/2 ; n>1 } are also the indices for which A020500(k)=Phi[k](1) is prime.
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LINKS
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Index entries for cyclotomic polynomials, values at X
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FORMULA
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A138929(n) = 2 A000961(n)
A138929 = {2} union { k | Phi[k](-1)=A020513(k) is prime } = {2} union { 2k | Phi[k](1)=A020500(k) is prime }
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PROGRAM
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(PARI) print1(2); for( i=1, 999, isprime( polcyclo(i, -1)) & print1(", ", i)) /* use ...subst(polcyclo(i), x, -2)... in PARI < 2.4.2. It should be more efficient to calculate a(n) as 2*A000961(n) ! */
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CROSSREFS
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Cf. A000961, A020513, A138920-A138940.
Sequence in context: A006586 A022292 A087370 this_sequence A113293 A080431 A122642
Adjacent sequences: A138926 A138927 A138928 this_sequence A138930 A138931 A138932
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KEYWORD
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nonn
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AUTHOR
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M. F. Hasler (www.univ-ag.fr/~mhasler), Apr 04 2008
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