A015853 Numbers k such that phi(k) | sigma(k + 9).

1, 2, 3, 4, 5, 6, 10, 12, 13, 14, 21, 24, 26, 30, 31, 37, 42, 45, 48, 50, 57, 60, 68, 76, 78, 96, 105, 111, 133, 156, 168, 175, 181, 196, 200, 215, 273, 286, 288, 290, 310, 320, 336, 350, 361, 369, 381, 399, 406, 420, 450, 465, 543, 585, 600, 612, 656, 740

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 1..1000

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), this sequence (m=9), A015856 (m=10), A015858 (m=11), A015859 (m=12), A015860 (m=13).

Programs

Magma

[n: n in [1..900] | DivisorSigma(1,n+9) mod EulerPhi(n) eq 0]; // G. C. Greubel, Dec 13 2018

Mathematica

Select[Range[1000], Divisible[DivisorSigma[1,#+9], EulerPhi[#]] &] (* Amiram Eldar, Dec 13 2018 *)

PARI

is(n)=!(sigma(n+9)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

Extensions

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