Is 1 a prime number?
Dr Dillion Mayhew, from Te Kura Mātai Tatauranga—School of Mathematics and Statistics answers:
"A common definition of a prime number is that it can only be divided by 1 and the number itself. For example:
- 13 is prime, because the only numbers that divide into 13 are 1 and 13 itself.
- 6 is not prime, because it can be divided by 2 and 3 as well as 1 and 6.
Using this definition, 1 can be divided by 1 and the number itself, which is also 1, so 1 is a prime number.
However, modern mathematicians define a number as prime if it is divided by exactly two numbers. For example:
- 13 is prime, because it can be divided by exactly two numbers, 1 and 13.
- 6 is not prime, because it can be divided by four numbers, 1, 2, 3 and 6.
1 can only be divided by one number, 1 itself, so with this definition 1 is not a prime number.
It is important to remember that mathematical definitions develop and evolve. Throughout history, many mathematicians considered 1 to be a prime number although that is not now a commonly held view. So when debating if 1 is a prime number, I'm prepared to call it a draw."
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