45 (number)

Template:Infobox number 45 (forty-five) is the natural number following 44 and preceding 46.

In mathematics

45 (in orange) as the difference of two nonzero squares in three different ways: 7²-2², 9²-6² and 23²-22².

45 is a composite number and a Størmer number.

Forty-five is conjectured to be the Ramsey number $R(5,5)$.

$\varphi (45)=\varphi (\sigma (45))$

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

Forty-five is a triangular number: it 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

45 years of marriage is marked by the sapphire wedding anniversary.

In the International Baccalaureate Diploma Programme, the number 45 is the maximum possible score.