A067261 Numbers n such that sigma(n+1)=3*phi(n).

1, 4, 5, 9, 10, 21, 32, 34, 45, 55, 65, 68, 70, 129, 153, 160, 176, 183, 203, 245, 340, 370, 407, 441, 550, 580, 635, 741, 765, 806, 845, 965, 1011, 1025, 1089, 1166, 1247, 1292, 1505, 1508, 1840, 2271, 2402, 2584, 2590, 3285, 3604, 4065, 4223, 4832, 5339

Offset: 1

Author

Benoit Cloitre, Feb 21 2002

Keywords

• nonn

Links

• Robert Israel, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A000010, A000203.

Programs

Maple

select(n -> numtheory:-sigma(n+1)=3*numtheory:-phi(n), [$1..10000]); # Robert Israel, May 29 2018

Mathematica

Select[Range[6000],DivisorSigma[1,#+1]==3*EulerPhi[#]&] (* Harvey P. Dale, Jun 11 2017 *)

PARI

isok(n) = sigma(n+1) == 3*eulerphi(n); \\ Michel Marcus, May 29 2018