OFFSET
1,2
COMMENTS
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..269
Hugo Pfoertner, Illustration of sequence terms for n<=5000, omitting n in A291790.
EXAMPLE
a(38)=53: Starting with k=38 produces the trajectory 38 -> 39 -> 50 -> 53 -> 53 ...
a(42)=144: See example in A290001.
MATHEMATICA
With[{lim = 100}, TakeWhile[#, # > 0 &] &@ Table[Which[Length@ # < lim, Last@ #, SameQ @@ Take[#, -2], Last@ #, True, 0] &@ NestWhileList[(DivisorSigma[1, #] + EulerPhi[#])/2 &, n, EvenQ@ DivisorSigma[1, #] &, 1, lim], {n, 270}]] (* Michael De Vlieger, Sep 06 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Sep 06 2017
STATUS
approved