A078549 - OEIS

%I #13 Apr 11 2024 04:09:32

%S 749,1498,2247,2568,2889,2996,3745,3959,4494,5778,5992,6741,7490,7918,

%T 8876,8988,9416,9737,9994,11235,11556,11877,11984,12733,13482,14231,

%U 14445,14980,16264,17976,18404,19474,20223,20804,22363,22470,23112

%N Non-balanced numbers in A015771.

%H Amiram Eldar, <a href="/A078549/b078549.txt">Table of n, a(n) for n = 1..10000</a>

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

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

%o (PARI) is(n) = {my(f = factor(n), phi = eulerphi(f)); (sigma(f) % phi) && !(sigma(f, 13) % phi);} \\ _Amiram Eldar_, Apr 11 2024

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

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

%K nonn

%O 1,1

%A _Labos Elemer_, Dec 05 2002