45 (number)


45 is the natural number following 44 and followed by 46.

In mathematics

Forty-five is a triangular number, and in particular the sum of all the decimal digits. It is the smallest triangle number which can be written as the sum of two squares. It is also a hexagonal and 16-gonal number.
45 is the sixth positive integer with a prime factorization of the form p2q, with p and q being prime.
Since the greatest prime factor of 452 + 1 = 2026 is 1013, which is much more than 45 twice, 45 is a Størmer number.
In base 10, it is a Kaprekar number and a Harshad number.
45 is the smallest odd number that has more divisors than n+1 and that has a larger sum of divisors than n+1.
45 is conjectured R.

In science

Forty-five may also refer to: