For every positive integers let the number of all positive integers of . Determine all positive integers with the property: .
%V0
For every positive integers $n$ let $d(n)$ the number of all positive integers of $n$. Determine all positive integers $n$ with the property: $d^3(n) = 4n$.
Izvor: Međunarodna matematička olimpijada, shortlist 2000
Školjka 
let 
the number of all positive integers of 
.