A015860 - OEIS

%I #18 Sep 08 2022 08:44:40

%S 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 122,128,146,152,155,164,176,204,222,237,310,330,331,342,377,378,400,

%U 427,460,465,490,500,504,560,602,610,626,704,722,770,817,861

%N Numbers k such that phi(k) | sigma(k + 13).

%H G. C. Greubel, <a href="/A015860/b015860.txt">Table of n, a(n) for n = 1..500</a>

%t Select[Range[900], Mod[DivisorSigma[1, #+13], EulerPhi[#]]==0 &] (* _G. C. Greubel_, Dec 13 2018 *)

%o (PARI) is(n)=!(sigma(n+13)%eulerphi(n)) \\ _Charles R Greathouse IV_, Sep 25 2012

%o (Magma) [n: n in [1..900] | DivisorSigma(1,n+13) mod EulerPhi(n) eq 0]; // _G. C. Greubel_, Dec 13 2018

%Y 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 nonn

%O 1,2

%A _Robert G. Wilson v_

%E Missing a(1)=1 inserted by _Sean A. Irvine_, Dec 13 2018