644880 has 40 divisors (see below), whose sum is σ = 1999872. Its totient is φ = 171904.

The previous prime is 644869. The next prime is 644881. The reversal of 644880 is 88446.

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

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (644881) by changing a digit.

644880 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1104 + ... + 1583.

2⁶⁴⁴⁸⁸⁰ is an apocalyptic number.

644880 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

644880 is an abundant number, since it is smaller than the sum of its proper divisors (1354992).

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

644880 is a wasteful number, since it uses less digits than its factorization.

644880 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2703 (or 2697 counting only the distinct ones).

The product of its (nonzero) digits is 6144, while the sum is 30.

The square root of 644880 is about 803.0442079985. The cubic root of 644880 is about 86.3958674292.

The spelling of 644880 in words is "six hundred forty-four thousand, eight hundred eighty".