639998 has 8 divisors (see below), whose sum is σ = 1001808. Its totient is φ = 306064.

The previous prime is 639997. The next prime is 640007. The reversal of 639998 is 899936.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a Curzon number.

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 pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6911 + ... + 7002.

It is an arithmetic number, because the mean of its divisors is an integer number (125226).

2⁶³⁹⁹⁹⁸ is an apocalyptic number.

639998 is a deficient number, since it is larger than the sum of its proper divisors (361810).

639998 is a wasteful number, since it uses less digits than its factorization.

639998 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 13938.

The product of its digits is 104976, while the sum is 44.

The square root of 639998 is about 799.9987499990. The cubic root of 639998 is about 86.1772978331.

It can be divided in two parts, 6 and 39998, that added together give a palindrome (40004).

The spelling of 639998 in words is "six hundred thirty-nine thousand, nine hundred ninety-eight".