java - Big O analysis for this for loop

Question

 sum = 0;
 for (i = 1; i <= n; i++) {    //#1
   for (j = 1; j <= i * i; j++) {     //#2
      if (j % i == 0) {    //#3 
          for (k = 1; k <= j; k++) {   //#4
             sum++;
         }
     }
  } 

}

The above got me confusing

Suppose #1 runs for N times
    #2 runs for N^2 times
    #3 runs for  N/c since for N inputs N/c could be true conditions
    #4 runs for  N times

Therefore roughly I could be looking at O(N^5) . I am not sure. Please help clarify.

EDIT I was wondering the runtime at the if(j%i==0). Since it takes N^2 inputs from its parent loop it could be doing (N^2)/c executions instead of N/c

Answer 1

I would say its O(N^4) as its the same as.

 for (int i = 1; i <= n; i++)        //#1 O(n ...
   for (int j = i; j <= i * i; j+=i) //#2 ... * n ...
     for (int k = 1; k <= j; k++)    //#4 ... * n^2) as j ~= i^2
         sum++;

or

public static void main(String... args) {
    int n = 9000;
    System.out.println((double) f(n * 10) / f(n));
}

private static long f(long n) {
    long sum = 0;
    for (long i = 1; i <= n; i++)   //#1
        for (long j = 1; j <= i; j++) //#2
            sum += i * j; // # 4
    return sum;
}

prints

9996.667534360826

which is pretty close to 10^4