A015859 Numbers k such that phi(k) | sigma(k + 12).

1, 2, 3, 10, 12, 14, 15, 16, 18, 21, 26, 30, 35, 39, 42, 44, 54, 65, 75, 76, 90, 108, 123, 126, 153, 156, 165, 218, 234, 252, 270, 364, 366, 370, 396, 462, 474, 494, 508, 525, 540, 558, 615, 620, 630, 646, 702, 732, 814, 852, 858, 918, 980, 1022, 1044

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), this sequence (m=12), A015860 (m=13).

Programs

Magma

[n: n in [1..900] | DivisorSigma(1,n+12) mod EulerPhi(n) eq 0]; // G. C. Greubel, Dec 13 2018

Mathematica

Select[Range[1100],Divisible[DivisorSigma[1,#+12],EulerPhi[#]]&] (* Harvey P. Dale, Jun 01 2018 *)

PARI

is(n)=!(sigma(n+12)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

Extensions

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