63999 has 12 divisors (see below), whose sum is σ = 99736. Its totient is φ = 39312.

The previous prime is 63997. The next prime is 64007. The reversal of 63999 is 99936.

It is a Cunningham number, because it is equal to 40³-1.

It is not a de Polignac number, because 63999 - 2¹ = 63997 is a prime.

63999 is a modest number, since divided by 999 gives 63 as remainder.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (63997) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 157 + ... + 390.

2⁶³⁹⁹⁹ is an apocalyptic number.

63999 is a deficient number, since it is larger than the sum of its proper divisors (35737).

63999 is a wasteful number, since it uses less digits than its factorization.

63999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 566 (or 563 counting only the distinct ones).

The product of its digits is 13122, while the sum is 36.

The square root of 63999 is about 252.9802363822. The cubic root of 63999 is about 39.9997916656. Note that the first 3 decimals are identical.

Subtracting 63999 from its reverse (99936), we obtain a cube (35937 = 33³).

It can be divided in two parts, 6 and 3999, that added together give a triangular number (4005 = T₈₉).

The spelling of 63999 in words is "sixty-three thousand, nine hundred ninety-nine".