OFFSET
1,1
COMMENTS
Termination at the first step occurs if k>3 is a square or twice a square, i.e. if k is a term of A028982. So the sequence lists the numbers that end at a fraction but are not of one of these two forms.
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 1..101
Hugo Pfoertner, Table of n, a(n) for n = 1..1136 (values above first 101 terms are only guesses)
N. J. A. Sloane, Iterating some number-theoretic functions, Posting to Seqfan mailing list, Sep 3, 2017
EXAMPLE
42 is in the sequence because the following iteration reaches an odd sigma(k):
k sigma(k) phi(k)
42 96 12 k->(sigma(k)+phi(k))/2, (96+12)/2=54
54 120 18 k->(sigma(k)+phi(k))/2, (120+18)/2=69
69 96 44 ...
70 144 24 ...
84 224 24
124 224 60
142 216 70
143 168 120 k->(sigma(k)+phi(k))/2, (168+120)/2=144
144 403 48 sigma(144) is odd, iteration terminates
CROSSREFS
KEYWORD
nonn
AUTHOR
Hugo Pfoertner, Sep 03 2017
EXTENSIONS
b-file curtailed beyond last certain value, moved other values to a-file. - N. J. A. Sloane, Oct 01 2017
STATUS
approved