644980 has 48 divisors (see below), whose sum is σ = 1645056. Its totient is φ = 207360.

The previous prime is 644977. The next prime is 644999. The reversal of 644980 is 89446.

It is an Ulam number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2245 + ... + 2515.

It is an arithmetic number, because the mean of its divisors is an integer number (34272).

2⁶⁴⁴⁹⁸⁰ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644980, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (822528).

644980 is an abundant number, since it is smaller than the sum of its proper divisors (1000076).

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

644980 is a wasteful number, since it uses less digits than its factorization.

644980 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 304 (or 302 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 31.

The square root of 644980 is about 803.1064686578. The cubic root of 644980 is about 86.4003329320.

The spelling of 644980 in words is "six hundred forty-four thousand, nine hundred eighty".