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A057126 Numbers n such that 2 is a square mod n. 23
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
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. A087780 (number of solutions mod n).
Sequence in context: A032537 A072120 A247866 * A363026 A319250 A018349
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 28 05:39 EDT 2024. Contains 371235 sequences. (Running on oeis4.)