A028794 Nonsquares mod 81.
2, 3, 5, 6, 8, 11, 12, 14, 15, 17, 18, 20, 21, 23, 24, 26, 27, 29, 30, 32, 33, 35, 38, 39, 41, 42, 44, 45, 47, 48, 50, 51, 53, 54, 56, 57, 59, 60, 62, 65, 66, 68, 69, 71, 72, 74, 75, 77, 78, 80
Offset: 1
Crossrefs
Cf. A010442.
Programs
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Mathematica
Complement[Range[0, 80], PowerMod[Range[81], 2, 81]] (* Alonso del Arte, Dec 27 2019 *)
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Scala
(0 to 80).diff((1 to 81).map(n => (n * n) % 81)) // Alonso del Arte, Dec 27 2019