A067884 Numbers k such that k = phi(sigma(phi(sigma(phi(sigma(k)))))).

1, 2, 8, 12, 16, 24, 30, 128, 240, 720, 1200, 1536, 1860, 6912, 15552, 15840, 18144, 32768, 67392, 83160, 92160, 142560, 272160, 290304, 290400, 712800, 1140480, 1190400, 3345408, 3571200, 5702400, 14859936, 29719872, 50319360, 118879488, 2147483648, 3889036800

Offset

1,2

Links

Table of n, a(n) for n=1..37.

Mathematica

Select[Range[3*10^7], EulerPhi[DivisorSigma[1, EulerPhi[DivisorSigma[1, EulerPhi[ DivisorSigma[1, #]]]]]]==#&] (* Harvey P. Dale, Apr 02 2015 *)

Crossrefs

Cf. A000010, A000203.

Sequence in context: A176100 A285658 A284802 * A005880 A290608 A340690

Adjacent sequences: A067881 A067882 A067883 * A067885 A067886 A067887

Keyword

easy,nonn

Author

Benoit Cloitre, Mar 02 2002

Extensions

More terms from Robert Gerbicz, Sep 05 2002

a(34)-a(37) from Amiram Eldar, May 19 2022

Status

approved