Natural number $M$ has $6$ divisors, such that sum of them are equal to $3500$.Find the all values of $M$.
1. **Identify the possible forms of \( M \)**:
   - Since \( M \) has exactly 6 divisors, it must be of the form \( p^5 \) or \( p^2q \), where \( p \) and \( q \) are prime numbers. This is because:
     - If \( M = p^5 \), the divisors are \( 1, p, p^2, p^3, p^4, p^5 \).
     - If \( M = p^2q \), the divisors are \( 1, p, p^2, q, pq, p^2q \).

2. **Case 1: \( M = p^5 \)**:
   - The sum of the divisors is:
     \[
     1 + p + p^2 + p^3 + p^4 + p^5 = 3500
     \]
   - This is a geometric series with the sum:
     \[
     \frac{p^6 - 1}{p - 1} = 3500
     \]
   - Solving for \( p \):
     \[
     p^6 - 1 = 3500(p - 1)
     \]
   - Testing small prime values:
     - For \( p = 2 \):
       \[
       2^6 - 1 = 63 \quad \text{and} \quad 3500(2 - 1) = 3500 \quad \text{(not equal)}
       \]
     - For \( p = 3 \):
       \[
       3^6 - 1 = 728 \quad \text{and} \quad 3500(3 - 1) = 7000 \quad \text{(not equal)}
       \]
     - For \( p \geq 5 \), \( p^6 - 1 \) grows too large. Thus, no solution in this case.

3. **Case 2: \( M = p^2q \)**:
   - The sum of the divisors is:
     \[
     1 + p + p^2 + q + pq + p^2q = (1 + p + p^2)(1 + q) = 3500
     \]
   - Factorizing 3500:
     \[
     3500 = 2^2 \cdot 5^3 \cdot 7
     \]
   - Since \( 1 + p + p^2 \) is always odd, \( 1 + q \) must be even, implying \( q \) is odd.
   - Let \( 1 + q = 2k \), then:
     \[
     (1 + p + p^2) \cdot 2k = 3500 \implies (1 + p + p^2) \cdot k = 1750
     \]
   - Possible values for \( 1 + p + p^2 \) are factors of 1750:
     \[
     1 + p + p^2 \in \{1, 2, 5, 7, 10, 14, 25, 35, 50, 70, 125, 175, 250, 350, 875, 1750\}
     \]
   - Testing these values:
     - For \( 1 + p + p^2 = 7 \):
       \[
       p^2 + p - 6 = 0 \implies (p - 2)(p + 3) = 0 \implies p = 2 \quad (\text{since } p \text{ is prime})
       \]
       - Then:
         \[
         1 + q = \frac{3500}{1 + 2 + 4} = 500 \implies q = 499 \quad (\text{which is prime})
       \]
     - Other values do not yield prime \( p \).

4. **Conclusion**:
   - The only possible value of \( M \) is:
     \[
     M = 2^2 \cdot 499 = 1996
     \]

The final answer is \(\boxed{1996}\)