A065818 Numbers k such that 3*phi(k) = 2*sigma(k).

5, 119, 3553, 4147, 8323, 198679, 218569, 248501, 298129, 468809, 547261, 1098349, 1398061, 1947379, 1990417, 3076549, 3453289, 3994753, 6969529, 7690249, 8790439, 11905457, 13097327, 14346577, 14732011, 14988967, 15286973, 16145269, 20851493, 21622867, 23083081, 24924599, 26218777, 26326867

Offset: 1

Author

Labos Elemer, Nov 23 2001

Keywords

• nonn

Examples

			n = 3553, 3*phi(3553) = 8640 = 2*4320 = 2*sigma(3553).
		

Links

• Jud McCranie, Table of n, a(n) for n = 1..10000 (first 75 terms from Harry J. Smith)

Crossrefs

Cf. A000010, A000203, A062699, A065819.

Programs

Mathematica

Select[Range[20000000], 3EulerPhi[#] == 2DivisorSigma[1, #] &]  (* Harvey P. Dale, Apr 18 2011 *)

PARI

isok(k) = { 3*eulerphi(k) == 2*sigma(k) } \\ Harry J. Smith, Oct 31 2009

Extensions

a(22)-a(28) from Harry J. Smith, Oct 31 2009