I've created two sectionwise defined functions for these calculations. Probably someone came up with that before me but I havent found it in the forum so I will post them here
They may not be very useful without a calculator, but a computer should handle them well^^
LVL is the Level you want to enhance your unit to.
EXP(LVL) is the experience points needed to enhance your unit from to LVL
LVL^2 means LVL*LVL.
With this, the Experience needed to go from level a to level b is simply EXP(b)-EXP(a)
Of course this can be turned the other way around:
EXP is the amount of experience you want to feed to your unit.
LVL(EXP) is the level you can reach with EXP experience.
(number)^0.5 is the square root of the number .
LVL(EXP)=19/6 + (EXP/30-2351/36)^0.5
If your level a unit gets e experience it reaches level LVL(EXP(a)+e).
Have fun trying them out