644360640 has 448 divisors, whose sum is σ = 2668584960. Its totient is φ = 127733760.

The previous prime is 644360627. The next prime is 644360659. The reversal of 644360640 is 46063446.

It is a tau number, because it is divible by the number of its divisors (448).

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 1699971 + ... + 1700349.

Almost surely, 2^644360640 is an apocalyptic number.

644360640 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644360640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1334292480).

644360640 is an abundant number, since it is smaller than the sum of its proper divisors (2024224320).

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

644360640 is a wasteful number, since it uses less digits than its factorization.

644360640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 440 (or 430 counting only the distinct ones).

The product of its (nonzero) digits is 41472, while the sum is 33.

The square root of 644360640 is about 25384.2596898157. The cubic root of 644360640 is about 863.7266796641.

The spelling of 644360640 in words is "six hundred forty-four million, three hundred sixty thousand, six hundred forty".