639720428 has 6 divisors (see below), whose sum is σ = 1119510756. Its totient is φ = 319860212.

The previous prime is 639720407. The next prime is 639720449. The reversal of 639720428 is 824027936.

It is a happy number.

639720428 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 (639720407) and next prime (639720449).

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 79965050 + ... + 79965057.

It is an arithmetic number, because the mean of its divisors is an integer number (186585126).

Almost surely, 2^639720428 is an apocalyptic number.

It is an amenable number.

639720428 is a deficient number, since it is larger than the sum of its proper divisors (479790328).

639720428 is a wasteful number, since it uses less digits than its factorization.

639720428 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 159930111 (or 159930109 counting only the distinct ones).

The product of its (nonzero) digits is 145152, while the sum is 41.

The square root of 639720428 is about 25292.6951509720. The cubic root of 639720428 is about 861.6483744835.

The spelling of 639720428 in words is "six hundred thirty-nine million, seven hundred twenty thousand, four hundred twenty-eight".