PLease see the attached file.
I understand that the formula for f(n)
f(n) = the sum as d runs through n of µ(d)*F(n/d) by the inversion formula.
The answer I came up with when solving for f(72) was 6912 so I think I am off a bit somewhere...
mu(1)*2*72^2 + mu(2)*2*36^2 + mu(3)*2*24^2 + mu(6)*2*12^2 = f(72) = 6912
I am not sure I am fully understanding how to use mobius inversion formula correctly so any pointers who be appreciated. Thanks for you time!