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 A129805 Primes congruent to +-1 mod 18. 13
 17, 19, 37, 53, 71, 73, 89, 107, 109, 127, 163, 179, 181, 197, 199, 233, 251, 269, 271, 307, 359, 379, 397, 431, 433, 449, 467, 487, 503, 521, 523, 541, 557, 577, 593, 613, 631, 647, 683, 701, 719, 739, 757, 773, 809, 811, 827, 829, 863, 881, 883, 919, 937, 953, 971, 991 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS From Katherine E. Stange, Feb 03 2010: (Start) Equivalently, primes p such that the smallest extension of F_p containing the cube roots of unity also contains the 9th roots of unity. Equivalently, the primes p for which, if p^t = 1 mod 3, then p^t = 1 mod 9. Equivalently, primes congruent to +/-1 modulo 9. Membership or non-membership of the prime p in this sequence and sequence A002144 (primes congruent to 1 mod 4; equivalently, primes p such that the smallest extension of F_p containing the square roots of unity contains the 4th roots of unity) appear to determine the behavior of amicable pairs on the elliptic curve y^2 = x^3 + p (Silverman, Stange 2009). (End) Primes in A056020. - Reinhard Zumkeller, Jan 07 2012 Primes congruent to (1,17) mod 18. - Vincenzo Librandi, Aug 14 2012 Equivalently, primes such that p^2 == 1 (mod 9). - M. F. Hasler, Apr 16 2022 LINKS Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 Emma Lehmer, On special primes, Pac. J. Math., 118 (1985), 471-478. J. H. Silverman and K. E. Stange. Amicable pairs and aliquot cycles for elliptic curves, arxiv:0912.1831 [math.NT], 2009. MATHEMATICA Union[Join[Select[Range[-1, 3000, 18], PrimeQ], Select[Range[1, 3000, 18], PrimeQ]]] (* Vladimir Joseph Stephan Orlovsky, Feb 18 2012 *) Select[Prime[Range[4000]], MemberQ[{1, 17}, Mod[#, 18]]&] (* Vincenzo Librandi, Aug 14 2012 *) PROG (Haskell) a129805 n = a129805_list !! (n-1) a129805_list = [x | x <- a056020_list, a010051 x == 1] -- Reinhard Zumkeller, Jan 07 2012 (Magma) [ p: p in PrimesUpTo(1300) | p mod 18 in {1, 17} ]; // Vincenzo Librandi, Aug 14 2012 (PARI) select( {is_A129805(n)=n^2%9==1&&isprime(n)}, primes(199)) \\ M. F. Hasler, Apr 16 2022 CROSSREFS Cf. A000040, A010051. Cf. A129806, A129807. Sequence in context: A144214 A191043 A306510 * A289492 A262286 A108024 Adjacent sequences: A129802 A129803 A129804 * A129806 A129807 A129808 KEYWORD nonn,easy AUTHOR N. J. A. Sloane, May 22 2007 STATUS approved

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Last modified June 3 14:22 EDT 2023. Contains 363116 sequences. (Running on oeis4.)