Couldn't find this basic equation on here so I thought I would add here.
To caculate how much lp is needed to get desired level
x is desired skill level
z is current skill level
y is needed lp
y=(50x^2+50x)-(50z^2+50z)
eg
y=(50(5)^2+50(5))-(50(1)^2+50(1))
y=1400
If you want to graph, only fill in current skill level.
Enjoy
edit: y=(50x^2+50x-100)-(50z^2+50z-100) to y=(50x^2+50x)-(50z^2+50z)
, where n is the final number in the series. Using this knowlege, you can find how much LP you need to get to n, and how much LP you have already put into a skill, x. Just subtract what you have already put in from what you are aiming for, multiply by 100, and bam, you got the amount required. For example, you need 504900 LP to level a skill from 1 to 100.