This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A078549 #13 Apr 11 2024 04:09:32
%S A078549 749,1498,2247,2568,2889,2996,3745,3959,4494,5778,5992,6741,7490,7918,
%T A078549 8876,8988,9416,9737,9994,11235,11556,11877,11984,12733,13482,14231,
%U A078549 14445,14980,16264,17976,18404,19474,20223,20804,22363,22470,23112
%N A078549 Non-balanced numbers in A015771.
%H A078549 Amiram Eldar, <a href="/A078549/b078549.txt">Table of n, a(n) for n = 1..10000</a>
%F A078549 sigma_13(a(n)) mod phi(a(n)) = 0; sigma(a(n)) mod phi(a(n)) <> 0.
%t A078549 q[n_] := Sign[Mod[DivisorSigma[{1, 13}, n], EulerPhi[n]]] == {1, 0}; Select[Range[24000], q] (* _Amiram Eldar_, Apr 11 2024 *)
%o A078549 (PARI) is(n) = {my(f = factor(n), phi = eulerphi(f)); (sigma(f) % phi) && !(sigma(f, 13) % phi);} \\ _Amiram Eldar_, Apr 11 2024
%Y A078549 Cf. A000010, A000203, A013961, A015771, A020492, A078539.
%Y A078549 Cf. A074866, A074868, A077801, A077803, A078544, A078550.
%K A078549 nonn
%O A078549 1,1
%A A078549 _Labos Elemer_, Dec 05 2002