45

is the integer between.

Math features

 * 45 is an odd number.
 * 45 is a composite number and a deficient number.
 * 45 is the first odd squareful number to be not a perfect power.
 * 45 is a triangular number. It is the $$\frac{\sqrt{8(45)+1}-1}{2}=9$$th triangular number. See triangular root.