Well done Fut. I was about to do it, as it is actually pretty simple to figure our once you see the X80 and X250 (20,000), then note the +first three digits, and divide by 2  (thus segragating the first 3 digits). Then the last four digits essentially X2, then divide by 2.

Fun stuff though.  I get a bigger kick out of little old axioms, like how to quickly tell if any number is evenly divisable by 3.  Just add up the digits, and if their sum is divisable by 3, the number is divisable by 3.  It's almost freaky! LOL   Calculus introduced me to even freakier stuff.  Two bad I don't remember any of it!  (the "two" is a literary pun).

SGE