45 (number)

← 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	$3^2 \cdot 5$
Divisors	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 (casually the sum of both digits is 9)(0 + 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. 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 2000 song by The Atomic Bitchwax, "Forty-Five"
• 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
• A football match consists of two periods of 45 minutes each.
• Guns or ammunition of .45 caliber. In the United States, "45" is often a reference to one of two specific .45 caliber cartridges— the .45 Colt or the .45 ACP.
• .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.