Keeping things equilateral, the internal angles (in degrees) to the number of side goes thusly:
3 60 4 90 5 108 6 120 7 128.571 8 135 9 140 10 144 11 147.273
three being a triangle, four a square, and so on. I made a curve with it with a spreadsheet

Keeping things equilateral, the internal angles (in degrees) to the number of side goes thusly:
3 60 4 90 5 108 6 120 7 128.571 8 135 9 140 10 144 11 147.273
three being a triangle, four a square, and so on. I made a curve with it with a spreadsheet

If you're asking for an expression for the angles in a regular polygon, then here you are:
If you walk along the edge, all the way around, you will have turned a total of $360^\circ$, so in each corner, you turn $\frac{360^\circ}{n}$. The internal angle is the supplementary angle of this, and is therefore $$ \left(180 -\frac{360}{n}\right)^\circ $$
Your regular $n$-gon can be cut into (non-regular) triangles by means of $n-2$ diagonals. Since the sum of internal angles in a triangle is $180^\circ$, the sum of internal angles in an $n$-gon is $(n-2)\cdot 180^\circ$ and the single angles are one $n$th thereof, i.e. $(1-\frac2n)\cdot 180^\circ$.