504

Number
$504$ (five hundred and four) is:


 * $2^3 \times 3^2 \times 7$


 * The first positive integer which can be expressed as the product of $2$ two-digit numbers in $2$ ways such that the factors in one of those pairs is the reversal of each of the factors in the other:
 * $504 = 12 \times 42 = 21 \times 24$