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 A291789 Trajectory of 270 under repeated application of k -> (phi(k)+sigma(k))/2. 7
 270, 396, 606, 712, 851, 852, 1148, 1416, 2032, 2488, 2960, 4110, 5512, 6918, 8076, 10780, 16044, 23784, 33720, 55240, 73230, 97672, 118470, 169840, 247224, 350260, 442848, 728448, 1213440, 2124864, 4080384, 8159616, 13515078, 15767596, 18626016, 29239504, 39012864, 62623600, 92580308 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The ultimate fate of this trajectory is presently unknown. It may reach a fractional value (when it dies), it may reach a prime (which would be a fixed point), it may enter a cycle of length greater than 1, or it may be unbounded. - Hugo Pfoertner and N. J. A. Sloane, Sep 18 2017 LINKS Sean A. Irvine, Table of n, a(n) for n = 0..515 [Terms through a(250) from Hugo Pfoertner, terms a(251)-a(356) from N. J. A. Sloane] N. J. A. Sloane, Three (No, 8) Lovely Problems from the OEIS, Experimental Mathematics Seminar, Rutgers University, Oct 05 2017, Part I, Part 2, Slides. (Mentions this sequence) MAPLE orbit:= proc(n, m) uses numtheory;   local V, k;   V:= Vector(m);   V[1]:= n;   for k from 2 to m do V[k]:= (sigma(V[k-1])+ phi(V[k-1]))/2 od:   convert(V, list) end proc: orbit(270, 200); # Robert Israel, Sep 07 2017 MATHEMATICA NestWhileList[If[! IntegerQ@ #, -1/2, (DivisorSigma[1, #] + EulerPhi@ #)/2] &, 270, Nor[! IntegerQ@ #, SameQ@ ##] &, 2, 38] (* Michael De Vlieger, Sep 19 2017 *) CROSSREFS Cf. A000010, A000203, A289997, A290001, A291790, A291787, A291804, A291805. See A291914 and A292108 for the "big picture". Sequence in context: A025393 A291790 A025394 * A292766 A180151 A278130 Adjacent sequences:  A291786 A291787 A291788 * A291790 A291791 A291792 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 03 2017 STATUS approved

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Last modified September 15 14:38 EDT 2019. Contains 327078 sequences. (Running on oeis4.)