A291791 - OEIS

%I #12 Sep 17 2017 19:58:14

%S 4,8,9,12,14,15,16,18,20,24,25,28,32,33,34,35,36,42,48,49,50,54,55,56,

%T 62,63,64,69,70,72,76,77,78,81,84,85,86,87,88,90,93,94,95,96,98,99,

%U 100,102,104,105,108,110,111

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

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

%H Hugo Pfoertner, <a href="/A291791/b291791.txt">Table of n, a(n) for n = 1..126</a>

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

%Y Cf. A000010, A000203.

%K nonn

%O 1,1

%A _N. J. A. Sloane_, Sep 03 2017

%E B-file shortened by _N. J. A. Sloane_, Sep 17 2017