644811820 has 12 divisors (see below), whose sum is σ = 1354104864. Its totient is φ = 257924720.

The previous prime is 644811809. The next prime is 644811823. The reversal of 644811820 is 28118446.

It is not an unprimeable number, because it can be changed into a prime (644811823) 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, 16120276 + ... + 16120315.

It is an arithmetic number, because the mean of its divisors is an integer number (112842072).

Almost surely, 2^644811820 is an apocalyptic number.

It is an amenable number.

644811820 is an abundant number, since it is smaller than the sum of its proper divisors (709293044).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

644811820 is a wasteful number, since it uses less digits than its factorization.

644811820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 32240600 (or 32240598 counting only the distinct ones).

The product of its (nonzero) digits is 12288, while the sum is 34.

The square root of 644811820 is about 25393.1451380092. The cubic root of 644811820 is about 863.9282258479.

The spelling of 644811820 in words is "six hundred forty-four million, eight hundred eleven thousand, eight hundred twenty".