639631291 has 4 divisors (see below), whose sum is σ = 688833712. Its totient is φ = 590428872.

The previous prime is 639631249. The next prime is 639631301. The reversal of 639631291 is 192136936.

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 639631291 - 2²⁷ = 505413563 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (639631231) 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, 24601191 + ... + 24601216.

It is an arithmetic number, because the mean of its divisors is an integer number (172208428).

Almost surely, 2^639631291 is an apocalyptic number.

639631291 is a deficient number, since it is larger than the sum of its proper divisors (49202421).

639631291 is a wasteful number, since it uses less digits than its factorization.

639631291 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 49202420.

The product of its digits is 52488, while the sum is 40.

The square root of 639631291 is about 25290.9329800227. The cubic root of 639631291 is about 861.6083526681.

The spelling of 639631291 in words is "six hundred thirty-nine million, six hundred thirty-one thousand, two hundred ninety-one".