639988 has 12 divisors (see below), whose sum is σ = 1127140. Its totient is φ = 317952.

The previous prime is 639983. The next prime is 639997. The reversal of 639988 is 889936.

It can be written as a sum of positive squares in 2 ways, for example, as 258064 + 381924 = 508^2 + 618^2 .

It is a congruent number.

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

639988 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 in 3 ways as a sum of consecutive naturals, for example, 358 + ... + 1186.

2⁶³⁹⁹⁸⁸ is an apocalyptic number.

It is an amenable number.

639988 is a deficient number, since it is larger than the sum of its proper divisors (487152).

639988 is a wasteful number, since it uses less digits than its factorization.

639988 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1026 (or 1024 counting only the distinct ones).

The product of its digits is 93312, while the sum is 43.

The square root of 639988 is about 799.9924999648. The cubic root of 639988 is about 86.1768489892.

The spelling of 639988 in words is "six hundred thirty-nine thousand, nine hundred eighty-eight".