A092584 Numbers k such that sigma(phi(k)) == phi(sigma(k)) (mod k), that is, A033632(k)/k is an integer.

1, 5, 9, 157, 225, 242, 516, 729, 3872, 13932, 14406, 17672, 18225, 20124, 21780, 29262, 29616, 45996, 65025, 76832, 92778, 95916, 106092, 106308, 114630, 114930, 121872, 125652, 140130, 140625, 145794, 149124, 160986, 179562, 185100, 234876

Offset: 1

Author

Labos Elemer, Mar 01 2004

Keywords

• nonn

Examples

			Includes but is not identical with A033632.
Below 10^7 only a(2) = 5 and a(4) = 157 give A033632(n)/n nonzero.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..2000

Crossrefs

Cf. A033632, A092585, A092586, A092587, A092588, A065395.

Programs

Mathematica

Select[Range[250000], Divisible[DivisorSigma[1, EulerPhi[#]] - EulerPhi[DivisorSigma[1, #]] , #] &]  (* Amiram Eldar, Mar 12 2020 *)

PARI

is(n)=sigma(eulerphi(n))==Mod(eulerphi(sigma(n)),n) \\ Charles R Greathouse IV, Nov 27 2013