A291791 Numbers n whose trajectory under the iteration of k -> (sigma(k)+phi(k))/2 reaches a fraction.

4, 8, 9, 12, 14, 15, 16, 18, 20, 24, 25, 28, 32, 33, 34, 35, 36, 42, 48, 49, 50, 54, 55, 56, 62, 63, 64, 69, 70, 72, 76, 77, 78, 81, 84, 85, 86, 87, 88, 90, 93, 94, 95, 96, 98, 99, 100, 102, 104, 105, 108, 110, 111

Offset: 1

Author

N. J. A. Sloane, Sep 03 2017

Keywords

• nonn

Comments

It would be nice to have an independent characterization of these numbers (not involving the map in the definition).

Links

• Hugo Pfoertner, Table of n, a(n) for n = 1..126

Crossrefs

Union of A028982 \ {1,2} and A290001. Also the complement of A289997.

Cf. A000010, A000203.

Extensions

B-file shortened by N. J. A. Sloane, Sep 17 2017