516 - Because thread page 22*516 post=11352! If you read 11352 as the opposite of it.... 25311. Take the first 25, that is 5*5. Put it at the end. (31155) Add 2 to the number before the first 5, Substract 2 from the first 5, add 2 to the second. (31337).
Now that is 31337. Pwnedz.
Samarkol