169

169 is a square: 13 x 13 = 169. Note that, in reverse order, 961 = 31².

169 is the smallest three-digit square whose digits are increasing. It is also the smallest square that is a prime number when turned upside down (691).

169 is the sum of seven consecutive primes: 13 + 17 + 19 + 23 + 29 + 31 + 37 = 169.

Add the factorials of its digits: 1! + 6! = 9! = 363,601. Repeat the process with 363,601 to get 3! + 6! + 3! + 6! + 0! + 1! = 1454. Repeat the process to get 169.

169 is the smallest square that is the difference of two cubes: 8³ – 7³ = 169.

169 has a representation as a sum of two squares: 169 = 5² + 12².

169 is the hypotenuse of a primitive Pythagorean triple: 169² = 119² + 120².

The number of nonequivalent starting hands in Texas hold ‘em poker is 169.

Sources: Number Gossip; Wikipedia