145 (number)

145 (one hundred [and] forty-five) is the natural number following 144 and preceding 146.

In mathematics

Although composite, 145 is a Fermat pseudoprime in sixteen bases with b < 145. In four of those bases, it is a strong pseudoprime: 1, 12, 17, and 144.
the Mertens function returns 0.^[1]
145 is a pentagonal number^[2] and a centered square number.^[3]
$145 = 1 2^{2} + 1^{2} = 8^{2} + 9^{2}$ . 145 is the fourth number that is the sum of two different pairs of squares. Also, 145 is the result of 3⁴ + 4³, making it a Leyland number.
$145 = 1! + 4! + 5!$ , making it a factorion.^[4] The only other numbers that have this property are 1, 2 and 40585.^[4]
$145 = 5^{2} + 5! = 1 1^{2} + 4! = 1 2^{2} + 1!$ , making 145 the smallest number that can be written as the sum of a square number and a factorial in 3 ways. The next number with this property is 46249.^[5]