639784 has 8 divisors (see below), whose sum is σ = 1199610. Its totient is φ = 319888.

The previous prime is 639757. The next prime is 639833. The reversal of 639784 is 487936.

It can be written as a sum of positive squares in only one way, i.e., 562500 + 77284 = 750^2 + 278^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a hoax number, since the sum of its digits (37) coincides with the sum of the digits of its distinct prime factors.

It is a nialpdrome in base 15.

It is an unprimeable number.

639784 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 as a sum of consecutive naturals, namely, 39979 + ... + 39994.

2⁶³⁹⁷⁸⁴ is an apocalyptic number.

It is an amenable number.

639784 is a deficient number, since it is larger than the sum of its proper divisors (559826).

639784 is a wasteful number, since it uses less digits than its factorization.

639784 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 79979 (or 79975 counting only the distinct ones).

The product of its digits is 36288, while the sum is 37.

The square root of 639784 is about 799.8649886075. The cubic root of 639784 is about 86.1676915543.

The spelling of 639784 in words is "six hundred thirty-nine thousand, seven hundred eighty-four".