OFFSET
1,2
COMMENTS
The iterated d function rapidly converges to fixed point 2. For k=4, the first n for which a(n)>2 is 60.
LINKS
Enrique PĂ©rez Herrero, Table of n, a(n) for n = 1..2000
FORMULA
a(n) = d(d(d(d(n)))).
EXAMPLE
E.g., n=96 and its successive iterates are 12,6,4,3 and 2. The 4th term is a(96)=3.
MATHEMATICA
f[n_]:=DivisorSigma[0, n]; Table[Nest[f, n, 4], {n, 100}] (* Vladimir Joseph Stephan Orlovsky, Mar 10 2010 *)
PROG
(PARI) a(n)=my(d=numdiv); d(d(d(d(n)))) \\ Charles R Greathouse IV, Apr 07 2012
CROSSREFS
KEYWORD
nonn
AUTHOR
STATUS
approved