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%I #22 Feb 20 2020 01:32:29
%S 0,1,4,9,16,20,24,25,36
%N Squares mod 40.
%t Union[PowerMod[Range[40], 2, 40]] (* _Vincenzo Librandi_, Dec 27 2019 *)
%o (Sage) [quadratic_residues(40)] # _Zerinvary Lajos_, May 24 2009
%o (Scala) (1 to 40).map(n => n * n % 40).toSet.toSeq.sorted // _Alonso del Arte_, Feb 20 2020
%Y Cf. A028753.
%K nonn,fini,full,easy
%O 1,3
%A _N. J. A. Sloane_