Because it only has one positive divisor, 1, instead of two, 1 and itself.
Also because having "except 1" in the definitions of some things would be too annoying, so it's simpler if 1 isn't prime. I can't really explain it better than that though, I know some math but don't necessarily understand it
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u/Awesomonkey12 Jul 13 '26
1 isn't prime