One day i got bored and was looking at my arms birthmarks and decided to count the amount of unique triangles i could make with just 4 birthmarks, lets call them dots in the puzzle.
To clarify: a unique triangle uses three dots and at least 1 of them is different from the other triangles. (4 dots can make 4 triangles; 1234: 123,124,134,234)
After i was done i added a fifth dot and started counting again..
I figured there should be a formula to calculate it, and so it got me started on creating that formula. I had some fun creating it and i hope you will as well.
Create the formula and tell how many unique triangles 13 dots can make