Chapter R - Section R.3 - Exponents, Roots, and Order of Operations - R.3 Exercises - Page 29: 20

$a^{5}$

In algebra, exponents can be used to write products of repeated factors. Exponents take the form $a^{b}$, where $a$ is the repeated factor and $b$ is the amount of times that the factor is being multiplied by itself. In this case, a is being multiplied by itself 5 times. Therefore, $a\times a\times a\times a\times a=a^{5}$.