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 A015860 #18 Sep 08 2022 08:44:40 %S A015860 1,2,4,6,7,8,9,10,11,15,20,25,27,34,38,41,42,44,56,57,64,66,80,82,120, %T A015860 122,128,146,152,155,164,176,204,222,237,310,330,331,342,377,378,400, %U A015860 427,460,465,490,500,504,560,602,610,626,704,722,770,817,861 %N A015860 Numbers k such that phi(k) | sigma(k + 13). %H A015860 G. C. Greubel, <a href="/A015860/b015860.txt">Table of n, a(n) for n = 1..500</a> %t A015860 Select[Range[900], Mod[DivisorSigma[1, #+13], EulerPhi[#]]==0 &] (* _G. C. Greubel_, Dec 13 2018 *) %o A015860 (PARI) is(n)=!(sigma(n+13)%eulerphi(n)) \\ _Charles R Greathouse IV_, Sep 25 2012 %o A015860 (Magma) [n: n in [1..900] | DivisorSigma(1,n+13) mod EulerPhi(n) eq 0]; // _G. C. Greubel_, Dec 13 2018 %Y A015860 Cf. A015834 (m=1), A015837 (m=2), A015840 (m=3), A015841 (m=4), A015843 (m=5), A015844 (m=6), A015845 (m=7), A015851 (m=8), A015853 (m=9), A015856 (m=10), A015858 (m=11), A015859 (m=12), this sequence (m=13). %K A015860 nonn %O A015860 1,2 %A A015860 _Robert G. Wilson v_ %E A015860 Missing a(1)=1 inserted by _Sean A. Irvine_, Dec 13 2018