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A138940
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Indices n such that A019328(n) = Phi(n,10) is prime, where Phi is a cyclotomic polynomial.
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25
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2, 4, 10, 12, 14, 19, 23, 24, 36, 38, 39, 48, 62, 93, 106, 120, 134, 150, 196, 317, 320, 385, 586, 597, 654, 738, 945, 1031, 1172, 1282, 1404, 1426, 1452, 1521, 1752, 1812, 1836, 1844, 1862, 2134, 2232, 2264, 2667, 3750, 3903, 3927, 4274, 4354, 5877, 6022
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OFFSET
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1,1
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COMMENTS
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Unique period primes (A040017) are often of the form Phi(k,10) or Phi(k,-10).
Terms of this sequence which are the square of a prime, a(n)=p^2, are such that A252491(p) is prime. Apart from a(2)=2^2, there is no such term up to 26570. - M. F. Hasler, Jan 09 2015
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LINKS
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MATHEMATICA
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Select[Range[1000], PrimeQ[Cyclotomic[#, 10]] &] (* T. D. Noe, Mar 03 2012 *)
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PROG
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(PARI) for( i=1, 999, isprime( polcyclo(i, 10)) &&& print1( i", ")) /* for PARI < 2.4.2 use ...subst(polcyclo(i, x), x, 10)... */
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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a(51)-a(91) from Ray Chandler, Maksym Voznyy et al. (cf. Phi_n(10) link), ca. 2009
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STATUS
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approved
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