127

This number is a prime.

Maya Mohsin Ahmed of UC Davis found that the numbers in an 8-by-8 Franklin square can be described by 127 equations. When Benjamin Franklin (1706-1790) wasn't flying kites, the noted polymath found time to experiment with recreational mathematics. Among other things, he invented magic square variants that are constructed with nonnegative numbers and contain the following properties: the entries of each row and column add to a common (or magic) sum; half of each row or column sums to half of the magic sum; the four corner entries together with the four middle entries add to the magic sum; in addition, each of the "bent rows" (as Franklin called them) have the magic sum. We still do not know what method Franklin used to construct his squares, and leave it for the reader to find other interesting properties.