109

109 is a prime number.

109 has a representation as a sum of two squares: 109 = 3² + 10².

107 and 109 form a twin prime pair.

109 is the hypotenuse of a primitive Pythagorean triple: 109² = 60² + 91².

109 is a centered triangular number.

109 is the smallest number that contains more digits than its square: 109² = 11881.

109 is the smallest number that is palindromic in bases 5 (414) and 9 (131).

109 is the atomic number of the element meitnerium.

Source: Number Gossip