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 A090866 Primes p == 1 (mod 4) such that (p-1)/4 is prime. 15
 13, 29, 53, 149, 173, 269, 293, 317, 389, 509, 557, 653, 773, 797, 1109, 1229, 1493, 1637, 1733, 1949, 1997, 2309, 2477, 2693, 2837, 2909, 2957, 3413, 3533, 3677, 3989, 4133, 4157, 4253, 4349, 4373, 4493, 4517, 5189, 5309, 5693, 5717, 5813, 6173, 6197 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Same as Chebyshev's subsequence of the primes with primitive root 2, because Chebyshev showed that 2 is a primitive root of all primes p = 4*q+1 with q prime. If the sequence is infinite, then Artin's conjecture ("every nonsquare positive integer n is a primitive root of infinitely many primes q") is true for n = 2. - Jonathan Sondow, Feb 04 2013 REFERENCES Albert H. Beiler: Recreations in the theory of numbers. New York: Dover, (2nd ed.) 1966, p. 102, nr. 5. P. L. Chebyshev, Theory of congruences. Elements of number theory, Chelsea, 1972, p. 306. LINKS G. C. Greubel, Table of n, a(n) for n = 1..10000 FORMULA a(n) = 4*A023212(n) + 1. MATHEMATICA Select[Prime[Range[1000]], Mod[#, 4]==1 && PrimeQ[(#-1)/4] &] (* G. C. Greubel, Feb 08 2019 *) PROG (MAGMA) f:=[n: n in [1..2000] | IsPrime(n) and IsPrime(4*n+1)]; [4*f[n] + 1: n in [1..50]]; // G. C. Greubel, Feb 08 2019 (PARI) isok(p) = isprime(p) && !frac(q=(p-1)/4) && isprime(q); \\ Michel Marcus, Feb 09 2019 CROSSREFS Cf. A001122, A005385, A005596, A023212, A221981, A222008. Sequence in context: A244637 A162579 A286658 * A098062 A094481 A045637 Adjacent sequences:  A090863 A090864 A090865 * A090867 A090868 A090869 KEYWORD nonn AUTHOR Benoit Cloitre, Feb 12 2004 STATUS approved

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Last modified April 23 13:21 EDT 2021. Contains 343204 sequences. (Running on oeis4.)