639999 has 24 divisors (see below), whose sum is σ = 1010880. Its totient is φ = 388608.

The previous prime is 639997. The next prime is 640007. The reversal of 639999 is 999936.

639999 is a `hidden beast` number, since 639 + 9 + 9 + 9 = 666.

It is a Cunningham number, because it is equal to 800²-1.

It is not a de Polignac number, because 639999 - 2¹ = 639997 is a prime.

639999 is a modest number, since divided by 999 gives 639 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639997) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7147 + ... + 7235.

It is an arithmetic number, because the mean of its divisors is an integer number (42120).

2⁶³⁹⁹⁹⁹ is an apocalyptic number.

639999 is a deficient number, since it is larger than the sum of its proper divisors (370881).

639999 is a wasteful number, since it uses less digits than its factorization.

639999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 159 (or 156 counting only the distinct ones).

The product of its digits is 118098, while the sum is 45.

The square root of 639999 is about 799.9993749998. Note that the first 3 decimals coincide. The cubic root of 639999 is about 86.1773427172.

The spelling of 639999 in words is "six hundred thirty-nine thousand, nine hundred ninety-nine".