644747820 has 48 divisors (see below), whose sum is σ = 1806620928. Its totient is φ = 171806400.

The previous prime is 644747819. The next prime is 644747821. The reversal of 644747820 is 28747446.

It is an interprime number because it is at equal distance from previous prime (644747819) and next prime (644747821).

It is a hoax number, since the sum of its digits (42) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (644747821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 101745 + ... + 107895.

It is an arithmetic number, because the mean of its divisors is an integer number (37637936).

Almost surely, 2^644747820 is an apocalyptic number.

644747820 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644747820 is an abundant number, since it is smaller than the sum of its proper divisors (1161873108).

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

644747820 is a wasteful number, since it uses less digits than its factorization.

644747820 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7910 (or 7908 counting only the distinct ones).

The product of its (nonzero) digits is 301056, while the sum is 42.

The square root of 644747820 is about 25391.8849241249. The cubic root of 644747820 is about 863.8996421929.

The spelling of 644747820 in words is "six hundred forty-four million, seven hundred forty-seven thousand, eight hundred twenty".