15th

15th is the ordinal form of the number 15 used to indicate order or position in a sequence. It appears in dates, lists, rankings, and other contexts where items are numbered. In written form, it is expressed as 15th; when spoken, it is typically read as the fifteenth.

Representations include the Roman numeral XV and the English alphabetic position of the letter O, the 15th letter. In calendar terms, the 15th day of a month is commonly referred to as the fifteenth.

Historically, the term appears in references to the 15th century (1400s) and to constitutional and legal markers such as the 15th Amendment to the United States Constitution, ratified in 1870, which prohibits denying a citizen the right to vote based on race, color, or prior servitude. In the Roman calendar, the ides commonly fell on the 15th in March, May, July, and October.

Mathematically, 15 is a composite number (3 × 5) and the sum of the first five natural numbers, making it a triangular number. In binary it is 1111. It is not a prime, and it has several divisors including 1, 3, 5, and 15.