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 A221982 Primes p == 2 (mod 5) for which 4*p+1 is also prime. 2
 7, 37, 67, 97, 127, 277, 307, 487, 577, 727, 997, 1087, 1297, 1327, 1567, 1597, 1777, 1987, 2017, 2437, 2647, 2677, 2767, 2887, 3037, 3067, 3307, 3457, 3637, 3907, 4057, 4297, 4447, 4567, 4987, 5197, 5527, 5557, 6007, 6247, 6337, 6367, 6397, 6547, 6577, 7027, 7057, 7237, 7417, 7507, 7717, 7867 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The corresponding primes 4*p+1 are Chebyshev's subsequence A221981 of the primes with primitive root 10. REFERENCES P. L. Chebyshev, Theory of congruences. Elements of number theory, Chelsea, 1972, p. 306. R. K. Guy, Unsolved Problems in Number Theory, F9. LINKS Paolo P. Lava, Table of n, a(n) for n = 1..10000 P. Moree, Artin's primitive root conjecture - a survey, arXiv 2004, revised 2012, p. 1. FORMULA a(n) = (A221981(n) - 1)/4. EXAMPLE 7 is a member because 7 == 2 (mod 5) and 29 = 4*7 + 1 are both prime. MAPLE A221982:=proc(q) local n; for n from 1 to q do if isprime(n) and isprime(4*n+1) and (n mod 5)=2 then print(n) fi; od; end: A221982 (10000); # Paolo P. Lava, Feb 12 2013 MATHEMATICA Select[ Prime[ Range[1000]], Mod[#, 5] == 2 && PrimeQ[4 # + 1] &] CROSSREFS Cf. A001913, A006883, A045380, A106849, A221981, A222008. Sequence in context: A168003 A132231 A289353 * A104915 A089376 A337423 Adjacent sequences:  A221979 A221980 A221981 * A221983 A221984 A221985 KEYWORD nonn AUTHOR Jonathan Sondow, Feb 02 2013 STATUS approved

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Last modified May 17 12:55 EDT 2021. Contains 343971 sequences. (Running on oeis4.)