Positive Integers which are not Divisor Sum Values

Theorem
The following positive integers are not the values of the $\sigma$ function $\sigma \left({n}\right)$ for any $n$:
 * $2, 5, 9, 10, 11, 16, 17, 19, 21, 22, 23, 25, 26, 27, 29, 33, 34, 35, 37, 41, 43, 45, 46, 47, 49, 50, 51, 52, 53, 55, 58, 59, 61, 64, 65, \ldots$