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%I #13 Dec 24 2019 13:14:28
%S 2,3,5,6,7,8,10,11,12,13,14,15,17,18,19,20,21,22,23,24,26,27,29,30,31,
%T 32,33,34,35,37,38,39,41,42,43,44,45,46,47,48,50,51,53,54,55,56,57,58,
%U 59,60,61,62,63,65,66,67,68,69,70,71
%N Nonsquares mod 72.
%e x^2 = 27 mod 72 has no solutions, so 27 is in the sequence.
%e x^2 = 28 mod 72 has the following solutions: x = 10, x = 26, x = 46, x = 62. So 28 is not in the sequence.
%t Complement[Range[71], PowerMod[Range[71], 2, 72]] (* _Alonso del Arte_, Jan 14 2017 *)
%o (Scala) (0 to 71).diff((1 to 72).map(n => (n * n) % 72)) // _Alonso del Arte_, Dec 24 2019
%Y Cf. A010433.
%K nonn,fini,full,easy
%O 1,1
%A _N. J. A. Sloane_
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