A right triangle with perpendicular sides $a$ and $b$ and hypotenuse $c$ has the following properties:
$a = p^m$ and $b = q^n$ with $p$ and $q$ prime numbers and $m$ and $n$ positive integers, $c = 2k +1$ with $k$ a positive integer.
Determine all possible values of $c$ and the associated values of $a$ and $b$.
1. Given a right triangle with perpendicular sides \(a\) and \(b\) and hypotenuse \(c\), we have the following properties:
   \[
   a = p^m \quad \text{and} \quad b = q^n
   \]
   where \(p\) and \(q\) are prime numbers, \(m\) and \(n\) are positive integers, and \(c = 2k + 1\) with \(k\) a positive integer.

2. According to the Pythagorean theorem, we have:
   \[
   p^{2m} + q^{2n} = c^2
   \]
   Since \(c\) is odd, we can assume without loss of generality that \(p \leq q\).

3. If both \(p\) and \(q\) are odd, then \(c\) would be even, which contradicts the given information that \(c\) is odd. Therefore, one of \(p\) or \(q\) must be 2. We assume \(p = 2\) and \(q\) is an odd prime.

4. Hence, \((2^m, q^n, c)\) forms a primitive Pythagorean triple. This implies there exist two coprime integers \(s > t > 0\) such that \(s - t\) is odd and:
   \[
   (2st, s^2 - t^2, s^2 + t^2) = (2^m, q^n, c)
   \]

5. From the above, we have:
   \[
   2st = 2^m \quad \text{and} \quad s^2 + t^2 = c
   \]
   Since \(2st = 2^m\), we get:
   \[
   st = 2^{m-1}
   \]

6. Also, we have:
   \[
   s^2 - t^2 = q^n
   \]
   This can be factored as:
   \[
   (s - t)(s + t) = q^n
   \]

7. Since \(s\) and \(t\) are coprime and \(s - t\) and \(s + t\) are also coprime, we have:
   \[
   (s - t, s + t) = (1, q^n) \quad \text{or} \quad (q^n, 1)
   \]
   Without loss of generality, assume:
   \[
   s - t = 1 \quad \text{and} \quad s + t = q^n
   \]

8. Adding and subtracting these equations, we get:
   \[
   2s = q^n + 1 \quad \text{and} \quad 2t = q^n - 1
   \]
   Therefore:
   \[
   s = \frac{q^n + 1}{2} \quad \text{and} \quad t = \frac{q^n - 1}{2}
   \]

9. Since \(st = 2^{m-1}\), we substitute \(s\) and \(t\):
   \[
   \left(\frac{q^n + 1}{2}\right) \left(\frac{q^n - 1}{2}\right) = 2^{m-1}
   \]
   Simplifying, we get:
   \[
   \frac{(q^n + 1)(q^n - 1)}{4} = 2^{m-1}
   \]
   \[
   \frac{q^{2n} - 1}{4} = 2^{m-1}
   \]
   \[
   q^{2n} - 1 = 2^{m+1}
   \]

10. Since \(q\) is an odd prime, let \(q = 3\) (the smallest odd prime). Then:
    \[
    3^{2n} - 1 = 2^{m+1}
    \]
    For \(n = 1\):
    \[
    3^2 - 1 = 9 - 1 = 8 = 2^3
    \]
    Thus, \(m + 1 = 3\) which gives \(m = 2\).

11. Therefore, \(a = 2^2 = 4\) and \(b = 3^1 = 3\). The hypotenuse \(c\) is:
    \[
    c = \sqrt{a^2 + b^2} = \sqrt{4^2 + 3^2} = \sqrt{16 + 9} = \sqrt{25} = 5
    \]

Conclusion:
The only possible value of \(c\) is 5, where \((a, b) = (4, 3)\) or \((3, 4)\).

The final answer is \(\boxed{5}\).