00:01
So let's look and determine if each one of these are primes.
00:02
I might not do them in order.
00:03
Let's start with 111.
00:05
When we add 1 plus 1 plus 1, we get 3, which means this is divisible by 3, therefore not a prime.
00:12
So i'm going to mark it out.
00:14
1111.
00:15
Well, this is a little -known trick, that if you take 1 plus 1 is 2, and then you have the other ones, 1 plus 1 is 2, that's the thing of that is a positive 2 and a negative 2, that means it's divisible by 11.
00:30
So it is not going to be prime.
00:33
So let's look at the next number, 5207.
00:37
Well, let's see, if i add that, i get 14.
00:39
Nothing obvious there, so we're just going to put that one on hold.
00:43
223.
00:44
So if i look at that one, i'm saying nothing obvious there either.
00:48
That has to be 4, that has to be 5.
00:50
Can't tell anything with 3.
00:52
Let's put that one on hold.
00:54
613.
00:55
I have 74.
00:56
It's not divisible by 3.
00:59
Let's wait on that one...