What about it:
0 - 120 as it is
120 - 1494x
150 -1992x
200 -2991,5x
300+ 0,75x
So for example:
*300 lvl after calculation
300 -200 lvl
441084800 - 129389800 = 31169500 31169500 / 3 * 1,5 = 15584750
200lvl - 150lvl
129389800 - 54042300 = 75347500 75347500 / 4 * 2 = 37673750
150lvl - 120 lvl
54042300 - 27393800 = 26648500 26648500 / 8 * 4 = 13324250
300 lvl will be 15584750 + 37673750 + 13324250 + 27393800 = 93976550 = 179lvl
* 400 Level after calculation
93976550 + (1050779800 - 441084800)/2 * 1 = 93976550 + 304847500 = 398824050 = 290lvl
Those "strange" numbers are amount of exp on 400 lvl, 300 lvl etc.
Hope u got it ;p