181 (one hundred [and] eighty-one) is the natural number following 180 and preceding 182.
In mathematics
181 is prime, and a palindromic, strobogrammatic, and dihedral number in decimal. 181 is a Chen prime.
181 is a twin prime with 179, equal to the sum of five consecutive prime numbers: 29 + 31 + 37 + 41 + 43.
181 is the difference of two consecutive square numbers 91<sup>2</sup> – 90<sup>2</sup>, as well as the sum of two consecutive squares: 9<sup>2</sup> + 10<sup>2</sup>.
As a centered polygonal number, 181 is: