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%I #22 Dec 22 2019 03:36:56
%S 0,1,4,9,16,21,25,28,36,37,49,57,60,64,72,81
%N Squares mod 84.
%t Union[Mod[Range[84]^2, 84]] (* _Harvey P. Dale_, Jan 09 2011 *)
%o (Sage) [quadratic_residues(84)] # _Zerinvary Lajos_, May 28 2009
%o (Scala) (1 to 84).map(n => (n * n) % 84).toSet.toSeq.sorted // _Alonso del Arte_, Dec 21 2019
%Y Cf. A028797.
%K nonn,fini,full,easy
%O 1,3
%A _N. J. A. Sloane_