OFFSET
1,45
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(105) = #{15, 21, 35} = #{3*5, 3*7, 5*7} = 3.
MATHEMATICA
Table[Count[Divisors[n], _?(OddQ[#]&&PrimeOmega[#]==2&)], {n, 120}] (* Harvey P. Dale, May 05 2015 *)
a[n_] := Count[e = FactorInteger[n][[;; , 2]], _?(# > 1 &)] + (o = Length[e])*(o - 1)/2 - If[EvenQ[n], If[e[[1]] > 1, o, o - 1], 0]; Array[a, 100] (* Amiram Eldar, Jun 30 2022 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, May 02 2005
STATUS
approved