For SK it works with this formula:
80000+16000*(1,2^(X-200)-1)/(1,2-1) where X >= 200, and round the answer, no floor or ceil functions.
Sum of a geometric sequence for those interested ^^
As for XP...it's totally random it seems.
Missions work with this formula:
floor(<level> - (X*<level>*0.05)) for missions under your level
floor(<level> + (X*<level>*0.05)) for missions over your level
X can be 0,2,3,4,5 and 6. that makes 11 different qls on missions