A028792 Nonsquares mod 79.
3, 6, 7, 12, 14, 15, 17, 24, 27, 28, 29, 30, 33, 34, 35, 37, 39, 41, 43, 47, 48, 53, 54, 56, 57, 58, 59, 60, 61, 63, 66, 68, 69, 70, 71, 74, 75, 77, 78
Offset: 1
Examples
x^2 = 7 mod 79 has no solutions, hence 7 is in the sequence. x^2 = 8 mod 79 has the solutions x = 18 and x = 61, so 8 is not in the sequence.
Programs
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Magma
[n: n in [0..78] | not IsSquare(R! n) where R:= ResidueClassRing(79)]; // Vincenzo Librandi, Jan 23 2020
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Mathematica
Complement[Range[78], PowerMod[Range[78], 2, 79]] (* Alonso del Arte, Jan 15 2017 *)
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PARI
isok(n) = (n < 79) && (kronecker(n, 79) == -1); \\ Michel Marcus, Jan 15 2017
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PARI
isok(n) = (n < 79) && (! issquare(Mod(n, 79))); \\ Michel Marcus, Jan 15 2017
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Scala
(0 to 78).diff((1 to 79).map(n => n * n % 79)) // Alonso del Arte, Jan 22 2020
Formula
Legendre symbol (a(n)/79) = -1. - Alonso del Arte, Jan 15 2017