170

170 = 2 x 5 x 17.

170 is 10101010 in base 2 (binary). It is 2222 in base 4.

170 has two representations as a sum of two squares: 170 = 1² + 13² = 7² + 11².

170 is the smallest number that can be written as the sum of the squares of two distinct primes, where each of these primes is the square of a prime added to another prime: 170 = (2² + 3)² + (3² + 2)².

170 is the start of a record-breaking run of consecutive integers (170 to176) with an odd number of prime factors.

Each internal angle of a regular 36-sided polygon is 170 degrees.

(stolen from NumberADay who took it from Prime Curios!)