639664 has 10 divisors (see below), whose sum is σ = 1239380. Its totient is φ = 319824.

The previous prime is 639647. The next prime is 639671. The reversal of 639664 is 466936.

It is a d-powerful number, because it can be written as 6² + 3⁹ + 6⁷ + 9⁵ + 6⁷ + 4⁵ .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 19974 + ... + 20005.

It is an arithmetic number, because the mean of its divisors is an integer number (123938).

2⁶³⁹⁶⁶⁴ is an apocalyptic number.

It is an amenable number.

639664 is a deficient number, since it is larger than the sum of its proper divisors (599716).

639664 is a wasteful number, since it uses less digits than its factorization.

639664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 39987 (or 39981 counting only the distinct ones).

The product of its digits is 23328, while the sum is 34.

The square root of 639664 is about 799.7899724303. The cubic root of 639664 is about 86.1623039185.

The spelling of 639664 in words is "six hundred thirty-nine thousand, six hundred sixty-four".