99 (number)

99 is a natural number that follows 98 and precedes 100. It is the largest two-digit number in the base-10 numbering system. It is therefore commonly used as an upper limit when a two-digit value is needed, as in some forms and counting machines.

99 is a composite number, meaning it has divisors other than 1 and itself. Its divisors are 1, 3, 9, 11, 33, and 99. Its prime factorization is 3 × 3 × 11, or 3² × 11.

Mathematical properties

The sum of the digits of 99 is 9 + 9 = 18, which is divisible by 9. This confirms that 99 is divisible by 9, following the standard divisibility rule for 9. Furthermore, 99 is the product of 9 and 11, and is a repdigit—a number whose digits are all the same in base 10.

99 is equivalent to 100 − 1. For this reason it is commonly useful in mental arithmetic: multiplication by 99 can be simplified by multiplying the number by 100 and then subtracting the original number. For example: 47 × 99 = 4,700 − 47 = 4,653.

General use

In commercial systems, 99 appears in pricing strategies—for example, prices ending in 99 are thought to seem lower than the next whole number. Additionally, 99 is among the numbers used to indicate a very high level, approaching but not reaching 100 percent.

Representation in other number systems

In Somali, 99 is pronounced "sagaashan iyo sagaal" (ninety and nine). In Roman numerals it is written XCIX. In binary notation it is 1100011.