644401764 has 48 divisors (see below), whose sum is σ = 1743315840. Its totient is φ = 205460640.

The previous prime is 644401759. The next prime is 644401781. The reversal of 644401764 is 467104446.

644401764 is a `hidden beast` number, since 644 + 4 + 0 + 1 + 7 + 6 + 4 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

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, 127227 + ... + 132194.

It is an arithmetic number, because the mean of its divisors is an integer number (36319080).

Almost surely, 2^644401764 is an apocalyptic number.

It is an amenable number.

644401764 is an abundant number, since it is smaller than the sum of its proper divisors (1098914076).

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

644401764 is a wasteful number, since it uses less digits than its factorization.

644401764 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 259457 (or 259449 counting only the distinct ones).

The product of its (nonzero) digits is 64512, while the sum is 36.

The square root of 644401764 is about 25385.0697064239. The cubic root of 644401764 is about 863.7450540227.

The spelling of 644401764 in words is "six hundred forty-four million, four hundred one thousand, seven hundred sixty-four".