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 A087277 Numbers k such that the three second-degree cyclotomic polynomials x^2 + 1, x^2 - x + 1 and x^2 + x + 1 are simultaneously prime. 6
 2, 6, 90, 960, 1974, 2430, 2730, 2736, 6006, 6096, 6306, 7014, 11934, 14190, 18276, 18486, 21204, 24906, 24984, 25200, 27210, 35700, 38556, 39306, 40860, 44694, 45654, 47124, 49524, 51246, 53220, 56700, 58176, 63330, 63960, 72996, 76650, 80394, 85560 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS By Schinzel's hypothesis H, there are an infinite number of k that yield simultaneous primes. Note that the two first-degree cyclotomic polynomials, x-1 and x+1, yield the twin primes for the numbers in A014574. From Ryan Bresler and Russell Jarrett, May 03 2019: (Start) All these k, except k=2, are multiples of 6. Proof: Suppose k == 1 (mod 3); then we have   k^2 == 1 (mod 3),   k^2 + 1 == 2 (mod 3), and   k^2 + 1 + k == 0 (mod 3), so k^2 + 1 + k cannot be prime if k == 1 (mod 3). Now suppose k == 2 (mod 3); then   k^2 == 1 (mod 3),   k^2 + 1 == 2 (mod 3), and   k^2 + 1 - k == 0 (mod 3), so k^2 + 1 - k cannot be prime if k == 2 (mod 3) (with the exception of k=2, which yields k^2 + 1 - k = 2^2 + 1 - 2 = 4+1-2 = 3, which is prime). Now suppose k == 0 (mod 3); then   k^2 == 0 (mod 3) and   k^2 + 1 == 1 (mod 3), so k^2 + 1 + k == 1 (mod 3) and k^2 + 1 - k == 1 (mod 3). Therefore k^2 + 1, k^2 + 1 + k and k^2 + 1 - k can all be prime only if k=2 or k == 0 (mod 3). Finally, if k == 1 (mod 2) for k > 2, then we have   k^2 == 1 (mod 2), and   k^2 + 1 == 0 (mod 2), so k^2 + 1 cannot be prime if k == 1 (mod 2). Now suppose k == 0 (mod 2); then   k^2 + 1 == 1 (mod 2),   so k^2 + 1 + k == 1 (mod 2) and k^2 + 1 - k == 1 (mod 2). Therefore, for k > 2, k == 0 (mod 2) and k == 0 (mod 3) must be satisfied for k^2 + 1, k^2 + 1 + k and k^2 + 1 - k to all be prime. (End) REFERENCES Paulo Ribenboim, The New Book of Prime Number Records, Springer, 1996, p. 391. Paulo Ribenboim, The Little Book of Bigger Primes, Springer, Second Edition, 2000, pp. 256-259. LINKS T. D. Noe, Table of n, a(n) for n = 1..1000 Eric W. Weisstein, MathWorld: Schinzel's Hypothesis Wikipedia, Schinzel's hypothesis H EXAMPLE 6 is a term of this sequence because 31, 37 and 43 are primes. MATHEMATICA x=0; Table[x=x+2; While[ !(PrimeQ[1+x^2] && PrimeQ[1+x+x^2] && PrimeQ[1-x+x^2]), x=x+2]; x, {50}] Join[{2}, Select[Range[6, 80000, 6], And@@PrimeQ[{#^2+1, #^2-#+1, #^2+#+1}]&]] (* Harvey P. Dale, Apr 07 2013 *) PROG (MAGMA) [m:m in [1..90000]| IsPrime(m^2+1) and IsPrime(m^2-m+1) and IsPrime(m^2+m+1) ]; // Marius A. Burtea, May 07 2019 CROSSREFS Cf. A014574 (first degree solutions: average of twin primes). Cf. A231612 (similar, but with fourth-degree cyclotomic polynomials). Cf. A231613 (similar, but with sixth-degree cyclotomic polynomials). Cf. A231614 (similar, but with eighth-degree cyclotomic polynomials). Cf. A233512 (similar, but increasing number of cyclotomic polynomials). Sequence in context: A305598 A179214 A128265 * A177861 A218151 A007188 Adjacent sequences:  A087274 A087275 A087276 * A087278 A087279 A087280 KEYWORD nonn AUTHOR T. D. Noe, Aug 27 2003 STATUS approved

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Last modified August 24 18:12 EDT 2019. Contains 326295 sequences. (Running on oeis4.)