27

27 = 3³, a perfect cube.

27 is the largest number that is the sum of the digits of its cube: 27³ = 19683; 1 + 9 + 6 + 8 + 3 = 27.

27 is the only number that is three times the sum of its digits.

27 is 11011 in base 2 (binary) and 33 in base 8.

27 is the smallest number with two representations as a sum of three squares: 27 = 1² + 1² + 5² = 3² + 3² + 3².

27 is the number of integer partitions of 15 into distinct parts.

The chemical element cobalt has atomic number 27.

Source: Number Gossip