OFFSET
1,2
COMMENTS
It seems that 9 is the only composite term.
a(2)-a(14) appear in De Koninck's book.
a(2)-a(18) were calculated by Kim & Bayad.
REFERENCES
J.-M. De Koninck, Those Fascinating Numbers, Amer. Math. Soc., 2009, page 54, entry 193.
LINKS
Daeyeoul Kim and Abdelmejid Bayad, Polygon Numbers Associated with the Sum of Odd Divisors Function, Experimental Mathematics, Vol. 26, No. 3 (2017), pp. 287-297.
EXAMPLE
MATHEMATICA
oddsigma[n_] := If[ n < 1, 0, Times @@ (If[ # < 3, 1, (#^(#2 + 1) - 1) / (# - 1)] & @@@ FactorInteger @ n)]; niter[n_] := Module[{c=0}, m=n; While[m>1, m = oddsigma[m]; c++]; c]; seq={}; sm=-1; Do[s=niter[n]; If[s>sm, AppendTo[seq, n]; sm=s], {n, 1, 10000}]; seq (* after Michael Somos at A000593 *)
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Amiram Eldar, Oct 29 2018
EXTENSIONS
a(19)-a(22) from Giovanni Resta, Oct 29 2018
STATUS
approved