forty-five

← 44 46 → 45
← 40 41 42 43 44 45 46 47 48 49 → List of numbers — Integers 0 10 20 30 40 50 60 70 80 90 →
Cardinal	forty-five
Ordinal	45th (forty-fifth)
Factorization
Prime	1, 3, 5, 9, 15, 45
Roman numeral	XLV
Binary	1011012
Octal	558
Duodecimal	3912
Hexadecimal	2D16

45 (forty-five) is the natural number following 44 and followed by 46.

In mathematics

Forty-five is a triangular number, a hexagonal and 16-gonal number, a Kaprekar number, and a Harshad number.

45 is the sixth positive integer with a prime factorization of the form p²q, with p and q being prime.

33 is the aliquot sum of 45 and the aliquot sequence of 45 is (45,33,15,9,4,3,1,0).

Since the greatest prime factor of 45² + 1 = 2026 is 1013, which is clearly more than 45 twice, 45 is a Størmer number.

The sum of all the digits is 45 (1+2+3+4+5+6+7+8+9=45)

In science

• The atomic number of rhodium

Astronomy

• Messier object M45, a magnitude 1.4 open cluster in the constellation Taurus, also known as the Pleiades
• The New General Catalogue object NGC 45, a magnitude 10.6 spiral galaxy in the constellation Cetus
• The Saros number of the solar eclipse series which began on -1436 March 30 and ended on -156 May 7. The duration of Saros series 45 was 1280.1 years, and it contained 72 solar eclipses.
• The Saros number of the lunar eclipse series which began on -1369 August 19 and ended on 182 March 8. The duration of Saros series 45 was 1550.6 years, and it contained 87 lunar eclipses.

In music

45 rpm gramophone record

• A type of gramophone record classified by its revolution speed of 45 revolutions per minute (rpm)
• Included in the title of "45 and Fat", a 1996 song by Babybird
• The title of a 2002 song by Elvis Costello, "45", both referring to the 45 rpm singles and to the artist's age when he wrote the song, which was released when he was 47
• The title of a 2003 song by Shinedown, "45" see 45 (song)
• The title of a 2006 song by noodles, "45"
• The title of a 2007 song by Ryan Shaw, "Do the 45"
• The title of a 2007 song by The Saturday Knights, "45"
• The title of a 1982 album by Kino, 45
• Repeated continuously in the 1997 song "Brimful of Asha" by Cornershop

In other fields

Forty-five may also refer to:

• In years of marriage, the sapphire wedding anniversary.
• A card game: Forty-five
• I-45 is the designation for a US interstate highway in Texas, connecting the major cities of Dallas and Houston; it is also the shortest "primary" interstate highway (one ending in 0 or 5)
• The '45 refers to the 1745 Jacobite Rising in Great Britain
• 45 (book), a book of essays by record producer Bill Drummond, derived both from the speed of a pop single and from his age when he finished writing it
• Guns or ammunition of .45 Caliber
• .45 (film), a 2006 motion picture.
• +45 is the telephone dialing code for Denmark
• Forty Five (Doctor Who audio) a Big Finish 2008 audio play made for the forty fifth anniversary of the British science fiction television show Doctor Who.
• The number of the French department Loiret

Historical years

45 A.D., 45 B.C., 1945, 2045, etc.