Circle packing in an equilateral triangle
Circle packing in an equilateral triangle is a packing problem in discrete mathematics where the objective is to pack n unit circles into the smallest possible equilateral triangle. Optimal solutions have been proved for n ≤ 15, and for any triangular number of circles, and conjectures are available for n ≤ 34.
Source: Wikipedia — Circle packing in an equilateral triangle (CC BY-SA 4.0)