60 (number) geometry, it is the number of seconds in a minute, and the number of minutes in a degree. In normal space, the three interior angles of an equilateral triangle each measure 60 degrees, adding up to 180 degrees. Because it is divisible by the sum of its digits in base 10, it is a Harshad number. A number system with base 60 is called sexagesimal (the original meaning of "sexagesimal" is sixtieth). It is the smallest positive integer that is written with only the smallest and the largest digit of base 2 (binary), base 3 (ternary) and base 4 (quaternary).
Monochromatic triangle G2(V,E2) are triangle-free graphs, and false otherwise. This decision problem is NP-complete. The problem may be generalized to triangle-free edge coloring, finding an assignment of colors to the edges of a graph so that no triangle has all three edges given the same color. The monochromatic triangle problem is the special case of triangle-free edge-coloring when there are exactly two colors available. If there exists a two-color triangle-free edge coloring, then the edges of each color form the two sets E1 and E2 of the monochromatic triangle problem. Conversely, if the monochromatic triangle problem has a solution, we can use