[jacobolus]

Greek geometers (e.g. in Euclid's Elements, Book 7) define a "unit" to be 1 and "numbers" (arithmoi) to start from 2. https://mathcs.clarku.edu/~djoyce/java/elements/bookVII/book...

But in practice there are a bunch of propositions/proofs where 1 is treated as a number just like any other.

[lupire]

log(1)=0, so it's unavoidable to consider 1 a something at least slightly different from the other numbers, as much as 0 is.