159

159 is a natural number that follows 158 and precedes 160. It is odd and composite, with prime factorization 3 × 53. Consequently, its positive divisors are 1, 3, 53, and 159, making it a semiprime. The sum of its digits is 15, which explains its divisibility by 3.

In various numeral systems, 159 is represented as 10011111 in binary, 0x9F in hexadecimal, and 237 in octal. In Roman numerals, it is written as CLIX. It is not a perfect square or cube. The Euler totient φ(159) = 104, meaning there are 104 positive integers less than 159 that are coprime to 159.

159 AD was a year in the 2nd century of the Roman Empire, during the reign of Emperor Antoninus Pius (r. 138–161). This period falls within the broader era often referred to as the Pax Romana, a time of relative stability and expansion across the Roman provinces.

As a semiprime, 159 is of interest in basic number theory as an example of a composite number formed by the product of two distinct primes. Its simple factorization and multiple base representations make it a common illustrative value in arithmetic and introductory mathematics discussions.