When the centres of any three coins lie in the corners of an equilateral triangle of some size, such coins form an equilateral coin triangle. How many equilateral coin triangles of different sizes can you count in the figure?

The object of the puzzle now is to remove the minimum number of coins so that no equilateral coin triangles remain. In other words, centres of any three coins among those that remained don't lie in the corners of an equilateral triangle.

http://www.puzzles.com/PuzzlePlayground/CoinsAndTriangles/CoinsAndTriang...