63

is the integer between.

Math features

 * 63 is an odd number.
 * 63 is a composite number.
 * 63 is a Mersenne number.
 * 63 is a Harshad number.
 * 63 is a number which is 1 less than a square number. It is part of the sequence n² - 1.
 * 63 is the sum of divisors for 64, and factors for 32.