A115448 Numbers k such that phi(k) = sigma(phi(phi(k))).

1, 2, 29, 58, 1119, 1492, 2238, 20441, 20803, 40882, 41606, 550339, 550687, 552407, 553339, 557239, 568487, 573319, 579367, 581279, 584039, 589399, 593959, 644959, 646303, 653317, 655879, 669599, 676837, 823311, 823527, 826599, 829233, 830199, 830961, 835959

Offset

1,2

Links

Hiroaki Yamanouchi, Table of n, a(n) for n = 1..387

Mathematica

lst={}; Do[u = EulerPhi@n; If[u == DivisorSigma[1, EulerPhi@u], AppendTo[lst, n]], {n, 10^6}]; lst

Prog

(PARI)
for(n=1, 10^7, if(eulerphi(n)==sigma(eulerphi(eulerphi(n))), print1(n, ", "))) \\ Derek Orr, Sep 19 2014
(Magma) [n: n in [1..2*10^6] | EulerPhi(n) eq DivisorSigma(1, EulerPhi(EulerPhi(n)))]; // Vincenzo Librandi, Dec 25 2015

Crossrefs

Sequence in context: A367796 A142969 A281546 * A276169 A107161 A372932

Adjacent sequences: A115445 A115446 A115447 * A115449 A115450 A115451

Keyword

nonn

Author

Giovanni Resta, Jan 22 2006

Extensions

a(35)-a(36) from Hiroaki Yamanouchi, Sep 19 2014

Status

approved