639491903 has 4 divisors (see below), whose sum is σ = 645823608. Its totient is φ = 633160200.

The previous prime is 639491893. The next prime is 639491921. The reversal of 639491903 is 309194936.

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 639491903 - 2⁴ = 639491887 is a prime.

It is a super-2 number, since 2×639491903² = 817899788005122818, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639491003) 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, 3165701 + ... + 3165902.

It is an arithmetic number, because the mean of its divisors is an integer number (161455902).

Almost surely, 2^639491903 is an apocalyptic number.

639491903 is a deficient number, since it is larger than the sum of its proper divisors (6331705).

639491903 is a wasteful number, since it uses less digits than its factorization.

639491903 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6331704.

The product of its (nonzero) digits is 157464, while the sum is 44.

The square root of 639491903 is about 25288.1771387342. The cubic root of 639491903 is about 861.5457610929.

The spelling of 639491903 in words is "six hundred thirty-nine million, four hundred ninety-one thousand, nine hundred three".