639909 has 12 divisors (see below), whose sum is σ = 935116. Its totient is φ = 421632.

The previous prime is 639907. The next prime is 639911. The reversal of 639909 is 909936.

639909 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (639907) and next prime (639911).

It can be written as a sum of positive squares in 2 ways, for example, as 497025 + 142884 = 705^2 + 378^2 .

It is not a de Polignac number, because 639909 - 2¹ = 639907 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639907) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 507 + ... + 1239.

2⁶³⁹⁹⁰⁹ is an apocalyptic number.

It is an amenable number.

639909 is a deficient number, since it is larger than the sum of its proper divisors (295207).

639909 is a wasteful number, since it uses less digits than its factorization.

639909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 836 (or 833 counting only the distinct ones).

The product of its (nonzero) digits is 13122, while the sum is 36.

The square root of 639909 is about 799.9431229781. The cubic root of 639909 is about 86.1733029586.

The spelling of 639909 in words is "six hundred thirty-nine thousand, nine hundred nine".