Forty-five (45, XLV) is the natural number following forty-four and followed by forty-six. It is a triangular number.
Its divisors are 3, 9, 15 and 45. Its prime factorization is
45 is also:
- The atomic number of rhodium.
- The total of books in the Old Testament of the Holy Bible in the Catholic version if the Book of Lamentations is considered part of the Book of Jeremiah.
- In years of marriage, the sapphire wedding anniversary.
- In reference to vinyl records, 45 refers to a type of record by its revolution speed of 45 revolutions per minute (rpm). This record disc was usually about 1/2 the circumference of a full record, with a larger central spindle, and contained one song on each side which resulted in calling such records singles.
- The caliber of some handguns.
- a card game: Forty-five
- The code for international direct dial phone calls to Denmark.
- For the year 45 AD, see 45.