A078549 Non-balanced numbers in A015771.

749, 1498, 2247, 2568, 2889, 2996, 3745, 3959, 4494, 5778, 5992, 6741, 7490, 7918, 8876, 8988, 9416, 9737, 9994, 11235, 11556, 11877, 11984, 12733, 13482, 14231, 14445, 14980, 16264, 17976, 18404, 19474, 20223, 20804, 22363, 22470, 23112

Offset: 1

Author

Labos Elemer, Dec 05 2002

Keywords

• nonn

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A000010, A000203, A013961, A015771, A020492, A078539.

Cf. A074866, A074868, A077801, A077803, A078544, A078550.

Programs

Mathematica

q[n_] := Sign[Mod[DivisorSigma[{1, 13}, n], EulerPhi[n]]] == {1, 0}; Select[Range[24000], q] (* Amiram Eldar, Apr 11 2024 *)

PARI

is(n) = {my(f = factor(n), phi = eulerphi(f)); (sigma(f) % phi) && !(sigma(f, 13) % phi);} \\ Amiram Eldar, Apr 11 2024

Formula

sigma_13(a(n)) mod phi(a(n)) = 0; sigma(a(n)) mod phi(a(n)) <> 0.