A015860 Numbers k such that phi(k) | sigma(k + 13).

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, 122, 128, 146, 152, 155, 164, 176, 204, 222, 237, 310, 330, 331, 342, 377, 378, 400, 427, 460, 465, 490, 500, 504, 560, 602, 610, 626, 704, 722, 770, 817, 861

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..500

Crossrefs

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).

Programs

Magma

[n: n in [1..900] | DivisorSigma(1,n+13) mod EulerPhi(n) eq 0]; // G. C. Greubel, Dec 13 2018

Mathematica

Select[Range[900], Mod[DivisorSigma[1, #+13], EulerPhi[#]]==0 &] (* G. C. Greubel, Dec 13 2018 *)

PARI

is(n)=!(sigma(n+13)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

Extensions

Missing a(1)=1 inserted by Sean A. Irvine, Dec 13 2018