639986 has 4 divisors (see below), whose sum is σ = 959982. Its totient is φ = 319992.

The previous prime is 639983. The next prime is 639997. The reversal of 639986 is 689936.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 534361 + 105625 = 731^2 + 325^2 .

It is not an unprimeable number, because it can be changed into a prime (639983) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 159995 + ... + 159998.

2⁶³⁹⁹⁸⁶ is an apocalyptic number.

639986 is a deficient number, since it is larger than the sum of its proper divisors (319996).

639986 is a wasteful number, since it uses less digits than its factorization.

639986 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 319995.

The product of its digits is 69984, while the sum is 41.

The square root of 639986 is about 799.9912499521. The cubic root of 639986 is about 86.1767592199.

The spelling of 639986 in words is "six hundred thirty-nine thousand, nine hundred eighty-six".