5. Write the numbers 1 and 2 on the blackboard. New numbers can be added in the following way: if the numbers $a$ and $b$ are on the blackboard, then the number $ab + a + b$ can be added. Can the number 12,131 be obtained using these methods?
(Tip: Let $c+1=a b+a+b+1=(a+1)(b+1)$. If we consider adding 1 to the numbers on the blackboard, then each new number is the product of the original numbers, i.e., originally 1 and 2, we consider 2 and 3, so after several operations, it becomes $2^{n} \cdot 3^{m}$. The original number is $2^{n} \cdot 3^{m}-1$, and 12131 does not have this form. )