Kabir says 1 is a prime number, because its factors are just 1 and itself

Why

Kabir is close to the definition but has slipped on one word. A prime number is one that has EXACTLY TWO different factors: 1 and the number itself. For 7, those two are 1 and 7 — two different numbers. For 1, the factors are '1 and itself', but itself IS 1, so that is only one distinct factor, not two. Because 1 does not have two different factors, it fails the definition of prime; and since it is not made by multiplying smaller numbers, it is not composite either — it sits on its own. Test it: list the factors of the first few numbers — 2 has {1, 2}, 3 has {1, 3}, 5 has {1, 5}, each exactly two; 1 has just {1}, exactly one. His sister is right: a prime has exactly two different factors, and 1 has only one, so 1 is neither prime nor composite.