639540709 has 4 divisors (see below), whose sum is σ = 639592416. Its totient is φ = 639489004.

The previous prime is 639540701. The next prime is 639540751. The reversal of 639540709 is 907045936.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 639540709 - 2³ = 639540701 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (639540701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4872 + ... + 36094.

It is an arithmetic number, because the mean of its divisors is an integer number (159898104).

Almost surely, 2^639540709 is an apocalyptic number.

It is an amenable number.

639540709 is a deficient number, since it is larger than the sum of its proper divisors (51707).

639540709 is a wasteful number, since it uses less digits than its factorization.

639540709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51706.

The product of its (nonzero) digits is 204120, while the sum is 43.

The square root of 639540709 is about 25289.1421167267. The cubic root of 639540709 is about 861.5676782496.

The spelling of 639540709 in words is "six hundred thirty-nine million, five hundred forty thousand, seven hundred nine".