MovieChat Forums > Billy Madison (1995) Discussion > Since when is the #1 NOT a prime number?

Since when is the #1 NOT a prime number?

posted 14 years ago by cup_a_tea_88
6 replies | jump to latest

So I was reading the goofs on for this movie, and one of them said Ms. Vaughn was teaching her students about prime numbers and she left off 2(which I agree is a goof) and she added 1. Since when is 1 not a prime number? I don't remember this in any of my math classes from high school. Now I will admit, its been 5 years since I took a high school math class...but I think I know a thing or too about such trivial things...when did this change? Because it sure as heck confuses the heck out of me...thanks in advance :)

[–] dma-maillist 14 years ago

1 is excluded from the prime numbers because if it were considered prime, no number at all would ever be prime.

It's kind of hard to explain and this will probably need clarification but we can see that 7 has only itself as a factor and 1. Essentially, we say that it is just itself, the number 7.

With the number 1 we can say that it is not prime if we consider it prime (it's kind of paradoxical). That is 1 * 1 is 1. But, 1 * 1 * 1 * 1 is also still just one. You can do this with any number. 7 is 7 * 1 * 1.

Because 1 can be used as a factor multiple times it would render every number not prime.

You can't do this with other numbers.

After all, 2 is not 1 * 2* 2* 2 even if 2 is 2 * 1 * 1.

So, one is just excluded from being prime.

So, it is not a goof in the movie.

[–] cup_a_tea_88 14 years ago

Ok...that makes sense...I guess I need to go back to 3rd grade :D lol thanks for the answer... :)

[–] wakanasakai 11 years ago

The explanation given by dma-maillist is wrong because it confuses communicativity with associativity. The truth is that both 1 & 2 are primes, & having both of them be primes doesn't prevent any other numbers from also being prime.
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[–] dma-maillist 10 years ago

Yeah, you're right in a way. I think I was just trying to think outside the box or something. I can't remember what I was doing at the time I wrote that.

But, generally speaking, 1 is excluded from prime because the general definition is a number that has itself and a 1 as factors. I suppose one can say that 1 has ONLY itself as a factor, which is different than other primes. 2 is 2 * 1. 3 is 3 * 1. 5 is 5 * 1. 7 is 7 * 1.

There are always TWO distinct factors for 2 on up for prime numbers.

But, with 1, there is only one distinct factor. Simply number 1.

2 can be 2 * 1 * 1 * 1....

There will still be only 2 distinct factors, even if 1 is multiplied an infinite amount of times. There will always be the digit 2 as a factor and 1 as another.

Whereas 1 is simply itself. It can be 1 * 1 * 1 on into infinity, but it still is simply, no other factor besides the digit 1.

I think that is what I was trying to illustrate but I don't think I did it correctly

But, that is what I meant, I think.

Thanks.

[–] toldyousew 10 years ago

A prime number is a positive integer that has exactly two distinct positive integer divisors.

Character is revealed by how you treat people with no power.

[–] recklessluke 14 years ago

I was taught that 1 is the 'identity number', and while it shares characteristics of a prime, it isn't. For all the reasons the guy above me says.