45 (number)

45 (forty-five) is the natural number following 44 and preceding 46.The number 45 is an odd composite number (3²×5), recognized as the 9th triangular number and a Kaprekar number.

← 44 45 46 →
← 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	32 × 5
Divisors	1, 3, 5, 9, 15, 45
Greek numeral	ΜΕ´
Roman numeral	XLV, xlv
Binary	1011012
Ternary	12003
Senary	1136
Octal	558
Duodecimal	3912
Hexadecimal	2D16

In mathematics

45 as the difference of two nonzero squares (in orange)

45 is a composite number and a Størmer number.

Forty-five is conjectured from Ramsey number $R(5,5)$.

$\phi (45)=\phi (\sigma (45))$

Forty-five degrees is half of a right angle (90°).

Forty-five is the sum of all single-digit decimal digits: $0+1+2+3+4+5+6+7+8+9=45$. It is, equivalently, the ninth triangle number. Forty-five is also the fourth hexagonal number and the second hexadecagonal number, or 16-gonal number.

In music

45 rpm gramophone record

• A type of gramophone record classified by its rotational speed of 45 revolutions per minute (rpm)

In other fields

• 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.
• In years of marriage, the sapphire wedding anniversary.
• Issue 45 of The North Briton was thought to be seditious but its publisher, John Wilkes, was celebrated as a champion of liberty. The number 45 was used as a symbol of support for him. Banquets were held with a theme of 45 while many items were produced showing the number or featuring it in some way. For example, a wig was produced with 45 curls.