A015793 Numbers n such that phi(n) + 4 divides sigma(n).

6, 15, 21, 24, 30, 33, 39, 42, 51, 57, 66, 69, 78, 84, 87, 93, 96, 102, 108, 111, 114, 120, 123, 129, 138, 141, 159, 174, 175, 177, 183, 186, 201, 213, 219, 220, 222, 237, 246, 249, 258, 267, 282, 291, 303, 309, 318, 321, 327, 339, 350, 354, 366

Offset: 1

Author

Robert G. Wilson v

Keywords

• nonn

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1300

Programs

Mathematica

Select[Range[400],Divisible[DivisorSigma[1,#],EulerPhi[#]+4]&] (* Harvey P. Dale, Aug 05 2014 *)

PARI

is(n)=!(sigma(n)%eulerphi(n+4)) \\ Charles R Greathouse IV, Sep 25 2012