Question 13
Prove that there are infinitely many positive integers which can't be expressed as $a^{d(a)} + b^{d(b)}$ where $a$ and $b$ are positive integers.
For positive integer $a$ expression $d(a)$ denotes the number of positive divisors of $a$.
For positive integer $a$ expression $d(a)$ denotes the number of positive divisors of $a$.