# My IT teacher said, that the 1 is not a prime number! I'm shocked. Is this true?

it is true as per defintion please refer to

yup, its true 1 is not a prime number =)

It is true. The definition of a prime number is an integer greater than 1 which has only 1 and itself as factors.

The number 1 is a special case which is considered neither prime nor composite, Although the number 1 used to be considered a prime it requires special treatment. A good reason not to call 1 a prime number is that if 1 were prime, then the statement of the fundamental theorem of arithmetic would have to be modified since "in exactly one way" would be false because

Its true.
By definition 1 is not a prime number, the smallest prime number is 2.
It has to do with making things work nicely.
For example every positive integer can be expressed UNIQUELY as a multiplication of prime numbers
for example 10=2 times 5
27=3 times 3 times 3
etc.
but if we allowed 1 to be a prime number then decomposition would not be unique.

Why be shocked? Thats the definition necessary to make every other rule work properly. Thats the same reason that any number raised to the zero power is 1. Does it make sense ? Only if you see what trouble is created if its not defined that way.

it is true yes ;(

yes it is

Don't be shocked. It's only the way we use words, and it doesn't affect the properties of the numbers themselves.

The odd primes 3, 5, 7, 11, 13, ... are an interesting set of numbers with a great many properties in common which they do not share with other numbers.

2 shares a lot of these properties but by no means all of them. So, in some mathematics, we have to say "the odd primes" instead of "the primes" when it is about something that is not true for 2. Mathematicians who work a lot with the odd primes might wish that they could just say "the primes", and make everybody else say "the primes and 2", but it's too late for that.

The number 1 shares so few of the properties of 2 and the odd primes that if it was called a prime, mathematicians would over and over again be saying "the primes, except for 1", and would hardly ever be able to say anything useful about "the primes".

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