List the factors

The question

Factors of 16

so far:116

so far:12816

so far:124816

Factors come in pairs — every one you find gives you a second. So work in from both ends.
1 × 16 = 16, so 1 and 16 are both factors.
2 × 8 = 16, so 2 and 8 are both factors.
4 × 4 = 16, so 4 pairs with itself — that is the middle, and there is nothing past it.
The pair has met in the middle, so the list is finished: 1, 2, 4, 8, 16. 5 factors.

How it works.

01
Factors come in pairs — every one you find gives you a second. So work in from both ends.
02
1 × 16 = 16, so 1 and 16 are both factors.
03
2 × 8 = 16, so 2 and 8 are both factors.
04
4 × 4 = 16, so 4 pairs with itself — that is the middle, and there is nothing past it.
05
The pair has met in the middle, so the list is finished: 1, 2, 4, 8, 16. 5 factors.