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.
145 is a pentagonal number and a centered square number.
145
=
12
2
+
1
2
=
8
2
+
9
2
{\displaystyle 145=12^{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
!
{\displaystyle 145=1!+4!+5!}
, making it a factorion. The only other numbers that have this property are 1, 2 and 40585.
145
=
5
2
+
5
!
=
11
2
+
4
!
=
12
2
+
1
!
{\displaystyle 145=5^{2}+5!=11^{2}+4!=12^{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.