00:01
So they give us the statement that pn being n squared plus n plus 11 is prime.
00:08
And what they want us to do is show that this is true for the first nine numbers, but is not true for 10.
00:15
So let's just go ahead and make a little chart for this.
00:19
So i'll have n here and then pn down here.
00:25
So let's see.
00:25
When we plug 1 into n squared plus n plus 11, that should give us.
00:34
13 or actually instead of putting pn down here let's put that actual function so n squared plus in plus 11 so when n is 1 we get an output of 13 13 is a prime number 2 let's go ahead and plug that in that gives 17 also prime 3 gives 23 which is prime 4 gives 31 which is prime 5 is 41 also prime 6 is 53 prime 7 is 67 which is prime 8 is 83 which is prime 9 is 101 which is prime so we've shown that all of these are prime and you could actually try to find numbers that divide these if you want you might be here for a while.
01:41
So if you do want to check, kind of a quick way to do it is to take the square root of all these numbers and then just divide by numbers smaller than it.
01:49
So if you wanted to check if 101 was actually prime or not, so you would do square root of 101.
01:54
So this is going to be about like 10 .1 something.
01:58
So all you would need to do is check 101 divided by 10, 101 divided by 9, 101 divided by 8, 101 divided by 7...