Given a number, click everything that divides it.
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A target number appears with a grid of candidates. Click every number that divides the target exactly. Factors come in pairs — if 4 divides 36 then so does 9 — so finding one hands you another for free.
That pairing is why you only need to search up to the square root. Everything above it is already accounted for by a partner below it.
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Yes. Every number has itself and 1 as factors, and both are included in the grid when they appear.
Factors always come in pairs multiplying to the target. Spot 3 in 36 and you immediately have 12. Working up to the square root finds every pair exactly once.
Times tables run forwards from a factor to a product. This runs backwards from a product to its factors, which is the harder and more useful direction.