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 A057126 Numbers n such that 2 is a square mod n. 18
 1, 2, 7, 14, 17, 23, 31, 34, 41, 46, 47, 49, 62, 71, 73, 79, 82, 89, 94, 97, 98, 103, 113, 119, 127, 137, 142, 146, 151, 158, 161, 167, 178, 191, 193, 194, 199, 206, 217, 223, 226, 233, 238, 239, 241, 254, 257, 263, 271, 274, 281, 287, 289, 302, 311, 313, 322 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers that are not multiples of 4 and for which all odd prime factors are congruent to +/- 1 mod 8. - Eric M. Schmidt, Apr 20 2013 Apparently the same as the list of numbers primitively represented by the indefinite quadratic form x^2 - 2y^2 (cf. A035251). - N. J. A. Sloane, Jun 11 2014 LINKS T. D. Noe, Table of n, a(n) for n=1..1000 N. J. A. Sloane et al., Binary Quadratic Forms and OEIS (Index to related sequences, programs, references) MAPLE with(numtheory); [seq(mroot(2, 2, p), p=1..300)]; MATHEMATICA ok[n_] := Reduce[ Mod[2 - k^2, n] == 0, k, Integers] =!= False; Prepend[ Select[ Range[400], ok], 1] (* Jean-François Alcover, Sep 20 2012 *) PROG (PARI) isok(n) = issquare(Mod(2, n)); \\ Michel Marcus, Feb 19 2016 CROSSREFS Includes the primes in A038873 and these (primes congruent to {1, 2, 7} mod 8) are the prime factors of the terms in this sequence. Cf. A008784, A057125, A057127, A057128, A057129, A057757, A035251, A038873. Cf. A087780 (number of solutions mod n). Sequence in context: A032537 A072120 A247866 * A319250 A018349 A256798 Adjacent sequences:  A057123 A057124 A057125 * A057127 A057128 A057129 KEYWORD nonn AUTHOR Henry Bottomley, Aug 10 2000 EXTENSIONS Checked by T. D. Noe, Apr 19 2007 STATUS approved

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Last modified March 23 04:46 EDT 2019. Contains 321422 sequences. (Running on oeis4.)