A067160 Numbers k such that sigma(phi(sigma(k))) = phi(sigma(phi(k))).

1, 13, 65, 157, 173, 193, 1093, 1201, 1843, 2231, 2753, 3665, 12707, 13829, 15269, 19549, 19813, 20003, 31601, 32069, 32201, 34001, 58091, 72971, 77681, 80745, 91505, 112241, 129899, 153409, 153851, 180521, 187777, 200413, 250961, 261313, 278513, 305761

Offset: 1

Author

Benoit Cloitre, Feb 19 2002

Keywords

• nonn

Comments

Are there any even terms in the sequence?

12 of the first 1000 terms are even. - Donovan Johnson, Mar 01 2013

Links

• Amiram Eldar, Table of n, a(n) for n = 1..5000 (terms 1..1000 from Donovan Johnson)

Crossrefs

Cf. A000010, A000203, A066175, A163370, A163372.

Programs

Mathematica

Select[Range[300000], DivisorSigma[1, EulerPhi[DivisorSigma[1, #]]] == EulerPhi[DivisorSigma[1, EulerPhi[#]]] &] (* Amiram Eldar, May 14 2022 *)

PARI

c=0; for(n=1, 242207369, if(sigma(eulerphi(sigma(n)))==eulerphi(sigma(eulerphi(n))), c++; write("b067160.txt", c " " n))) /* Donovan Johnson, Mar 01 2013 */

Extensions

Edited by Dean Hickerson, Feb 20 2002