173 (number)

173 is a natural number that comes after 172 and before 174. It is an odd number, meaning it cannot be divided by two.

The defining property of 173 is that it is a prime number, which is to say a number greater than 1 that has no divisors other than 1 and itself. Its only divisors are 1 and 173.

Mathematical properties

173 is the 40th prime number starting from 2. It is preceded by the prime 167 and followed by 179. Because 173 is the average of these two neighbouring primes—(167 + 179) ÷ 2 = 173—it is known as a balanced prime.

When 173 is doubled and one is added, the result is 347, which is also prime. For this reason, 173 belongs to the Sophie Germain primes. Additionally, 173 is one more than 4 squared, which means it can be written as the sum of two squares: 173 = 2² + 13² = 4 + 169.

173 is not part of a twin prime pair, since both 171 and 175 are composite: 171 = 9 × 19, and 175 = 5² × 7. When its digits are reversed, the result is 371, which equals 7 × 53, so 173 is not an emirp (a prime that remains prime when its digits are reversed).

Representation in other systems

In binary, 173 is written as 10101101. In hexadecimal, it is AD. In Roman numerals, it would be written as CLXXIII.