999 (number)

999 is a natural number in standard counting mathematics. It follows 998 and precedes 1000. In the decimal number system, 999 is the largest three-digit number; adding one converts it to four digits, namely 1000.

In Somali, it is read as "sagaal boqol sagaashan iyo sagaal" (nine hundred ninety-nine). All three of its digits are the same, making it one of the numbers known as repdigits—those where each digit is identical when written in base ten.

Mathematical properties

999 is not a prime number. Its prime factorization is 999 = 3 × 3 × 3 × 37, or equivalently 3³ × 37. Its divisors are 1, 3, 9, 27, 37, 111, 333, and 999. It is an odd number because it is not divisible by two.

The sum of its digits is 9 + 9 + 9 = 27, which means 999 is divisible by both 9 and 27. Additionally, 999 is one less than 1000, placing it close to powers of ten, making it useful in mental arithmetic: for example, 999 × n = 1000n − n.

When 1 is divided by 999, it yields a repeating decimal: 1/999 = 0.001001001..., where the three-digit pattern repeats. This property makes 999 a useful tool for converting repeating three-digit decimals into standard fraction form.

Common uses

In several countries, 999 is the telephone number for emergency services (police, fire, ambulance). The number also appears widely in pricing (prices ending in 999) and in numbered symbols, because it is close to a round number but slightly below it.