https://en.wikipedia.org/wiki/22_(number)
22 is a palindromic number and the eighth semiprime; its proper divisors are 1, 2, and 11. [2] [3] It is the second Smith number, the second Erdős–Woods number, and the fourth large Schröder number. [4] [5] [6] It is also a Perrin number, from a sum of 10 and 12