644556 has 48 divisors (see below), whose sum is σ = 1733760. Its totient is φ = 184320.

The previous prime is 644549. The next prime is 644557. The reversal of 644556 is 655446.

It is not an unprimeable number, because it can be changed into a prime (644557) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 2380 + ... + 2636.

It is an arithmetic number, because the mean of its divisors is an integer number (36120).

2⁶⁴⁴⁵⁵⁶ is an apocalyptic number.

644556 is a gapful number since it is divisible by the number (66) 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 644556, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (866880).

644556 is an abundant number, since it is smaller than the sum of its proper divisors (1089204).

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

644556 is a wasteful number, since it uses less digits than its factorization.

644556 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 294 (or 292 counting only the distinct ones).

The product of its digits is 14400, while the sum is 30.

The square root of 644556 is about 802.8424502977. The cubic root of 644556 is about 86.3813960287.

The spelling of 644556 in words is "six hundred forty-four thousand, five hundred fifty-six".