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A066651
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Primes of the form 2*s + 1, where s is a squarefree number (A005117).
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4
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3, 5, 7, 11, 13, 23, 29, 31, 43, 47, 53, 59, 61, 67, 71, 79, 83, 103, 107, 131, 139, 149, 157, 167, 173, 179, 191, 211, 223, 227, 229, 239, 263, 269, 277, 283, 293, 311, 317, 331, 347, 349, 359, 367, 373, 383, 389, 419, 421, 431
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OFFSET
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1,1
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COMMENTS
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For these odd primes delta(p) = A055034(n) = (p-1)/2 is squarefree, and therefore the (Abelian) multiplicative group Modd p (see a comment on A203571 for Modd n, not to be confused with mod n) is guaranteed to be cyclic. This is because the number of Abelian groups of order n (A000688) is 1 precisely for the squarefree numbers A005117. See also A210845. One can in fact prove that the multiplicative group Modd p is cyclic for all primes (the case p=2 is trivial). - Wolfdieter Lang, Sep 24 2012
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LINKS
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EXAMPLE
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MATHEMATICA
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Select[2 * Select[Range[200], SquareFreeQ] + 1, PrimeQ] (* Amiram Eldar, Feb 22 2021 *)
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PROG
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(PARI) isok(p) = isprime(p) && (p>2) && issquarefree((p-1)/2); \\ Michel Marcus, Feb 22 2021
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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