639684 has 24 divisors (see below), whose sum is σ = 1658720. Its totient is φ = 213192.

The previous prime is 639679. The next prime is 639689. The reversal of 639684 is 486936.

It is an interprime number because it is at equal distance from previous prime (639679) and next prime (639689).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a d-powerful number, because it can be written as 6 + 3¹² + 6² + 9⁵ + 8⁵ + 4⁷ .

It is not an unprimeable number, because it can be changed into a prime (639689) by changing a digit.

639684 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2854 + ... + 3069.

2⁶³⁹⁶⁸⁴ is an apocalyptic number.

It is an amenable number.

639684 is an abundant number, since it is smaller than the sum of its proper divisors (1019036).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

639684 is a wasteful number, since it uses less digits than its factorization.

639684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5936 (or 5928 counting only the distinct ones).

The product of its digits is 31104, while the sum is 36.

The square root of 639684 is about 799.8024756151. The cubic root of 639684 is about 86.1632019046.

The spelling of 639684 in words is "six hundred thirty-nine thousand, six hundred eighty-four".