This problem is inspired by the $$$9 \times 9$$$ multiplication table.

In my primary school, my math teacher always asked us to memorize which two one-digit numbers we can multiply to obtain some two-digit numbers, such as $$$12 = 2 \times 6 = 3 \times 4$$$, and $$$21 = 3 \times 7$$$, and so on. But she never asked us any questions like which two numbers we can multiply to obtain $$$60$$$, or $$$34$$$, because $$$60$$$ and $$$34$$$ are not the product of any two one-digit numbers.

In fact, $$$10$$$, $$$12$$$, $$$14$$$, $$$15$$$, $$$16$$$, $$$18$$$, $$$20$$$, $$$21$$$, $$$24$$$, $$$25$$$, $$$27$$$, $$$28$$$, $$$30$$$, $$$32$$$, $$$35$$$, $$$36$$$, $$$40$$$, $$$42$$$, $$$45$$$, $$$48$$$, $$$49$$$, $$$54$$$, $$$56$$$, $$$63$$$, $$$64$$$, $$$72$$$, and $$$81$$$, all can be expressed as the product of some two one-digit numbers.

(I’m not pretty sure if any similar problem has appeared at Codeforces … My friend said that he was familiar with my idea, and felt that this problem might have appeared in a Codeforces contest long ago.)