A015856 Numbers k such that phi(k) | sigma(k + 10).

1, 2, 3, 4, 5, 7, 12, 13, 14, 20, 28, 29, 32, 36, 44, 45, 52, 53, 56, 60, 66, 77, 84, 86, 104, 105, 108, 110, 123, 130, 144, 172, 221, 228, 238, 270, 287, 312, 342, 366, 380, 385, 396, 441, 468, 558, 584, 585, 588, 644, 672, 750, 754, 760, 854, 864

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), A015853 (m=9), this sequence (m=10), A015858 (m=11), A015859 (m=12), A015860 (m=13).

Programs

Magma

[n: n in [1..900] | DivisorSigma(1,n+10) mod EulerPhi(n) eq 0]; // G. C. Greubel, Dec 13 2018

Mathematica

Select[Range[1000], Divisible[DivisorSigma[1,#+10], EulerPhi[#]] &] (* Amiram Eldar, Dec 13 2018 *)

PARI

is(n)=!(sigma(n+10)%eulerphi(n)) \\ Charles R Greathouse IV, Sep 25 2012

Extensions

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