639947509 has 4 divisors (see below), whose sum is σ = 646545004. Its totient is φ = 633350016.

The previous prime is 639947471. The next prime is 639947519. The reversal of 639947509 is 905749936.

639947509 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It can be written as a sum of positive squares in 2 ways, for example, as 312228900 + 327718609 = 17670^2 + 18103^2 .

It is a cyclic number.

It is not a de Polignac number, because 639947509 - 2²³ = 631558901 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 (639947519) 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, 3298602 + ... + 3298795.

It is an arithmetic number, because the mean of its divisors is an integer number (161636251).

Almost surely, 2^639947509 is an apocalyptic number.

It is an amenable number.

639947509 is a deficient number, since it is larger than the sum of its proper divisors (6597495).

639947509 is an equidigital number, since it uses as much as digits as its factorization.

639947509 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6597494.

The product of its (nonzero) digits is 1837080, while the sum is 52.

The square root of 639947509 is about 25297.1838155950. The cubic root of 639947509 is about 861.7503152788.

The spelling of 639947509 in words is "six hundred thirty-nine million, nine hundred forty-seven thousand, five hundred nine".