Q:

Generate a self working EXP system for levels

I am making a small game in C# and I can't figure out how to make a self working EXP system that gets the EXP you need to level up by the players current level.
This is how I want it to work.
1 = 75
2 = 75 + 75 = 150
3 = 75 + 75 + 75 + 75 = 300
4 = 75 + 75 + 75 + 75 + 75 + 75 + 75 = 525

How would I go about doing this?

A:

It appears that your pattern is "add one 75, add two 75s, add three 75s"... This could be written mathematically as:
s_1 = 75
s_{n+1} = s_n + 75 * n

This means that you can use use
(1 + level * (level - 1) / 2) * 75

