199

199 is a natural number that comes after 198 and before 200. In decimal notation it is written as 199.

In mathematics, 199 is a prime number, and it is the 46th prime in the sequence of prime numbers. It is odd and not divisible by any integer other than 1 and itself. The sum of its digits is 19, which is also prime. Since 199 is congruent to 3 modulo 4, it cannot be expressed as a sum of two integer squares. An alternative geometric identity is that 199 equals the difference of consecutive squares: 199 = 100^2 − 99^2.

In different numeral systems, 199 is represented as 11000111 in binary, C7 in hexadecimal, and CXCIX in Roman numerals. It can also be written as 200 − 1 and, more generally, as a difference of consecutive squares, since any odd number can be written as the difference of n+1 squared and n squared.

As a year, 199 may refer to the year 199 CE (AD) in the common era or to 199 BCE in the before-common era. The year 199 CE falls within the reign of Roman Emperor Septimius Severus (193–211 CE), situating it in the late 2nd century of the Roman Empire.