644556720 has 40 divisors (see below), whose sum is σ = 1998126576. Its totient is φ = 171881728.

The previous prime is 644556709. The next prime is 644556727. The reversal of 644556720 is 27655446.

644556720 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (644556727) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1342587 + ... + 1343066.

Almost surely, 2^644556720 is an apocalyptic number.

644556720 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644556720 is an abundant number, since it is smaller than the sum of its proper divisors (1353569856).

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

644556720 is a wasteful number, since it uses less digits than its factorization.

644556720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2685669 (or 2685663 counting only the distinct ones).

The product of its (nonzero) digits is 201600, while the sum is 39.

The square root of 644556720 is about 25388.1216319758. The cubic root of 644556720 is about 863.8142819275.

The spelling of 644556720 in words is "six hundred forty-four million, five hundred fifty-six thousand, seven hundred twenty".