644544 has 56 divisors (see below), whose sum is σ = 1899920. Its totient is φ = 214272.

The previous prime is 644531. The next prime is 644549. The reversal of 644544 is 445446.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 644544.

It is not an unprimeable number, because it can be changed into a prime (644549) by changing a digit.

644544 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, 1542 + ... + 1914.

2⁶⁴⁴⁵⁴⁴ is an apocalyptic number.

644544 is a gapful number since it is divisible by the number (64) 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 644544, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (949960).

644544 is an abundant number, since it is smaller than the sum of its proper divisors (1255376).

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

644544 is a wasteful number, since it uses less digits than its factorization.

644544 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 394 (or 378 counting only the distinct ones).

The product of its digits is 7680, while the sum is 27.

The square root of 644544 is about 802.8349768165. The cubic root of 644544 is about 86.3808599578.

The spelling of 644544 in words is "six hundred forty-four thousand, five hundred forty-four".