644680 has 32 divisors (see below), whose sum is σ = 1477440. Its totient is φ = 253120.

The previous prime is 644671. The next prime is 644687. The reversal of 644680 is 86446.

644680 is a nontrivial binomial coefficient, being equal to C(1136, 2).

It is a super-3 number, since 3×644680³ = 803810817333696000, which contains 333 as substring. Note that it is a super-d number also for d = 2.

It is not an unprimeable number, because it can be changed into a prime (644687) 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, 2727 + ... + 2953.

It is an arithmetic number, because the mean of its divisors is an integer number (46170).

2⁶⁴⁴⁶⁸⁰ is an apocalyptic number.

644680 is the 1135-th triangular number and also the 568-th hexagonal number.

644680 is the 379-th centered nonagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 644680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (738720).

644680 is an abundant number, since it is smaller than the sum of its proper divisors (832760).

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

644680 is a wasteful number, since it uses less digits than its factorization.

644680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 309 (or 305 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 28.

The square root of 644680 is about 802.9196721964. The cubic root of 644680 is about 86.3869350387.

The spelling of 644680 in words is "six hundred forty-four thousand, six hundred eighty".