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Numbers m such that in Z/mZ the number of squares is equal to the number of invertible elements.
4

%I #8 Nov 11 2024 05:25:14

%S 1,3,4,12,70,90,210

%N Numbers m such that in Z/mZ the number of squares is equal to the number of invertible elements.

%C Numbers m such that A000224(m) = A000010(m).

%t f1[p_, e_] := Floor[p^(e+1)/(2p + 2)] + 1; f1[2, e_] := Floor[2^e/6] + 2; f[p_, e_] := f1[p, e]/((p-1) * p^(e-1)); q[1] = True; q[k_] := Times @@ f @@@ FactorInteger[k] == 1; Select[Range[210], q] (* _Amiram Eldar_, Nov 11 2024 *)

%Y Cf. A000010, A000224, A122904, A122905, A122906, A122907.

%K fini,full,nonn,changed

%O 1,2

%A _Max Alekseyev_, Sep 18 2006