Explanation:
it goes like this :
we start with 2 as the smallest prime number (and then go up to the next and the next prime number to check if it is a factor), and we end, when we reach 1 as final result.
816 ÷ 2 = 408
408 ÷ 2 = 204
204 ÷ 2 = 102
102 ÷ 2 = 51
51 ÷ 2 no
51 ÷ 3 = 17
17 ÷ 3 no
17 ÷ 5 no
17 ÷ 7 no
17 ÷ 11 no
17 ÷ 13 no
17 ÷ 17 = 1 finished
so,
816 = 2⁴×3×17
remember, we are looking only for prime numbers as factors. so, e.g. 9 or 15 are not prime numbers.