639987 has 4 divisors (see below), whose sum is σ = 853320. Its totient is φ = 426656.

The previous prime is 639983. The next prime is 639997. The reversal of 639987 is 789936.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 639987 - 2² = 639983 is a prime.

It is a D-number.

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

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106662 + ... + 106667.

It is an arithmetic number, because the mean of its divisors is an integer number (213330).

2⁶³⁹⁹⁸⁷ is an apocalyptic number.

639987 is a deficient number, since it is larger than the sum of its proper divisors (213333).

639987 is a wasteful number, since it uses less digits than its factorization.

639987 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 213332.

The product of its digits is 81648, while the sum is 42.

The square root of 639987 is about 799.9918749587. The cubic root of 639987 is about 86.1768041046.

It can be divided in two parts, 6 and 39987, that added together give a palindrome (39993).

The spelling of 639987 in words is "six hundred thirty-nine thousand, nine hundred eighty-seven".