A028740 -id:A028740 - cp's OEIS frontend

0, 1, 4, 7, 9, 10, 13, 16, 19, 22, 25

Offset: 1

Union[PowerMod[Range[27], 2, 27]] (* Alonso del Arte, Nov 27 2019 *)

[quadratic_residues(27)] # Zerinvary Lajos, May 24 2009

(1 to 27).map(n => n * n).map( % 27).toSet.toSeq.sorted // _Alonso del Arte, Nov 27 2019

2, 3, 5, 6, 8, 11, 12, 14, 15, 17, 18, 20, 21, 23, 24, 26, 29, 30, 32, 33, 35, 38, 39, 41, 42, 44, 45, 47, 48, 50, 51, 53

Offset: 1

Cf. A010415, A028740 (subsequence).

[ n: n in [0..53] | not IsSquare(R! n) where R:= ResidueClassRing(54)]; // Vincenzo Librandi, Dec 28 2019

Complement[Range[0, 53], PowerMod[Range[54], 2, 54]] (* Alonso del Arte, Dec 27 2019 *)

(0 to 53).diff((1 to 54).map(n => (n * n) % 54)) // Alonso del Arte, Dec 27 2019

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