Test your knowledge of taxicab geometry, triangular numbers, the golden ratio and more.

The number 153 is the 17th triangular number: this means that if you add the numbers from 1 to 17, you get 153. If you were to divide the 153 into equal points, you could form an equilateral triangle.

The number of angles is equal to the number of sides it has. Triangles ... have three sides, therefore they have three angles. Interior angles in a triangle sum to a half turn (180˚). Interior ...