173

173 is a natural number that follows 172 and precedes 174. In mathematics, it is notable for being a prime number.

It is the 40th prime. As a prime congruent to 1 modulo 4, 173 can be expressed as a sum of two squares: 173 = 13^2 + 2^2. It is also the sum of three consecutive primes: 53 + 59 + 61.

In numeral systems, 173 is written as decimal 173, binary 10101101, octal 255, and hexadecimal AD. In Roman numerals it is CLXXIII.

The number 173 may also appear as a year in historical dating, such as 173 CE or 173 BC, depending on the calendar system and era used. In number theory, 173 is sometimes referenced for its properties as a prime of the form 4k+1, which guarantees a representation as a sum of two squares. Overall, 173 is a small but interesting prime with multiple representations and simple algebraic properties.