285

285 = 3 x 5 x 19.

285 is the smallest number whose sum of distinct prime factors is an odd prime to the power of an odd prime: 3 + 5 + 19 = 27 = 3³.

285 is 555 in base 7.

285 is a square pyramidal number (the sum of all squares of integers from 1 to 9): 285 = 1² + 2² + 3² + 4² + 5² + 6² + 7² + 8² + 9².

285² = 81225 uses the same digits as 135² (18225) and 159² (25281).

285 is the number of binary rooted trees with 13 vertices.

Source: Prime Curios!