109 (number)

109 is a natural number that comes after 108 and before 110. It is an odd number and a prime number—divisible only by 1 and itself. In the decimal system, it is composed of three digits: one hundred, zero tens, and nine units.

Like other small numbers, 109 has useful applications in number theory, since prime numbers are fundamental to the factorization of integers. It also appears in measurement systems, numerical sequences, and chemical notation.

Mathematical properties

109 is a prime number. It is part of a twin prime pair with 107, since their difference is two. Compared with 113, the difference is four, making them cousin primes. The sum of its digits (1+0+9) is 10. Its square (109 × 109) is 11,881.

109 lies between 100 and 121—meaning its square root falls between 10 and 11, approximately 10.44. Also, 109 = 100 + 9, both of which are perfect squares (10² and 3²); numbers that are the sum of two perfect squares have special properties related to their factorization in other domains.

Use in other fields

In chemistry, 109 is the atomic number of meitnerium (Mt), a synthetic element with extremely limited stability. The number 109 is also used in road designations, facility names, and emergency telephone numbers in certain countries.

Notation of the number

In Roman numerals, 109 is written CIX. In binary, it is 1101101. In hexadecimal, it is 6D. In Somali, it is read as 'boqol iyo sagaal' (one hundred and nine).