644644 has 72 divisors (see below), whose sum is σ = 1608768. Its totient is φ = 221760.

The previous prime is 644629. The next prime is 644647. The reversal of 644644 is 446446.

644644 = T₂₃₁ + T₂₃₂ + ... + T₂₅₂.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644647) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 28017 + ... + 28039.

It is an arithmetic number, because the mean of its divisors is an integer number (22344).

2⁶⁴⁴⁶⁴⁴ 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 644644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (804384).

644644 is an abundant number, since it is smaller than the sum of its proper divisors (964124).

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

644644 is a wasteful number, since it uses less digits than its factorization.

644644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 65 (or 56 counting only the distinct ones).

The product of its digits is 9216, while the sum is 28.

The square root of 644644 is about 802.8972537006. The cubic root of 644644 is about 86.3853270122.

The spelling of 644644 in words is "six hundred forty-four thousand, six hundred forty-four".