One is not Prime/Proof 1
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The integer $1$ (one) is not a prime number.
By definition, a prime number is a positive integer which has exactly $2$ divisors which are themselves positive integers.
From Divisors of One, the only divisors of $1$ are $1$ and $-1$.
So the only divisor of $1$ which is a positive integer is $1$.
As $1$ has only one such divisor, it is not classified as a prime number.
- 1982: Martin Davis: Computability and Unsolvability (2nd ed.) ... (previous) ... (next): Appendix $1$: Some Results from the Elementary Theory of Numbers
- 1986: David Wells: Curious and Interesting Numbers ... (previous) ... (next): $1$
- 1997: David Wells: Curious and Interesting Numbers (2nd ed.) ... (previous) ... (next): $1$
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