639966 has 8 divisors (see below), whose sum is σ = 1279944. Its totient is φ = 213320.

The previous prime is 639959. The next prime is 639983. The reversal of 639966 is 669936.

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

639966 is an admirable number.

It is a congruent number.

It is an unprimeable number.

639966 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 3 ways as a sum of consecutive naturals, for example, 53325 + ... + 53336.

It is an arithmetic number, because the mean of its divisors is an integer number (159993).

2⁶³⁹⁹⁶⁶ is an apocalyptic number.

639966 is a primitive abundant number, since it is smaller than the sum of its proper divisors, none of which is abundant.

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

639966 is a wasteful number, since it uses less digits than its factorization.

639966 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 106666.

The product of its digits is 52488, while the sum is 39.

The square root of 639966 is about 799.9787497178. The cubic root of 639966 is about 86.1758615163.

The spelling of 639966 in words is "six hundred thirty-nine thousand, nine hundred sixty-six".