The number 1888081808881 is interesting on several counts. First, it’s a prime number, evenly divisible only by itself and 1. In base 10, it’s also a palindromic number. It has the same sequence of ...

Schools sometimes teach “fact families:” triangles that connect three numbers based on their sum and differences. For example, the triangle below expresses the series of relationships: 5 + 3 = 8, 8 - ...