(n+1)(n-1)

(n+1)(n-1) = n^2 - 1

Ahhh my good friends (n+1) and (n-1). I swear I must have factored n^2 - 1 a million times during various math classes.

But it's kind of cool that when you multiply n-1 and n+1 that you get n^2 - 1.

Like 3*5 = 15
or 15*17 = 255 (reminds me of CHS numbers for my old hard drive)
or 9*11 = 99
or 99*101 = 9999
or 9999*10001 = 99999999

The power of algebra.