591 = 3 x 197.
591 is the number of ways to stack 23 boxes in a line so that each box lies on the table or on a box next to two boxes.
591 is a divisor of 144 - 1.
591 is 303 in base 14.
591 is a number n such that n2 (349281) contains exactly six different digits (A054034).
591 is the sum of five distinct positive pentatope numbers (A104395).
Source: What's Special About This Number?