"It's just an interesting post number. End of a page. 50 twice, etc."
It's a great deal more than that!
It's the sum of all the numbers from one to one hundred.
Which is also a way to seem like a genius. If your grade-school teacher gives the class an assignment to add up all the numbers from one to one hundred, (and your name is Carl Friedrich Gauss), you simply add the first number (one) to the last number (one hundred).
This gives you one hundred and one.
Then you add the second number, (two) to the next to the last number, (ninety-nine), and you get another one hundred and one.
Continuing, the third number (three) added to the third from the last number (ninety-eight) provides ... one hundred and one.
Obviously, for young Gauss, this eventually yields fifty pairs of the number one-hundred-and-one, or to simplify ...
... 5050
Ta-freaking-da.
.
It's a cute trick, but just how useful is it, really?
Well, obviously, it isn't limited to just 1 to 100. You can use any sequence of numbers, (even an odd sequence, carry the one unpaired number in the middle!), pair them up, and multiply.
It's how to take a short cut, if you're a genius, or if you've heard of one.
Wow. Maths.
I took the Cubs outside and let them clobber one another with foam swords while running through the woods. Very successful meeting.