644028 has 96 divisors (see below), whose sum is σ = 2032128. Its totient is φ = 153600.

The previous prime is 644009. The next prime is 644029. The reversal of 644028 is 820446.

It is a junction number, because it is equal to n+sod(n) for n = 643989 and 644007.

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 644028.

It is not an unprimeable number, because it can be changed into a prime (644029) by changing a digit.

644028 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 31 ways as a sum of consecutive naturals, for example, 15688 + ... + 15728.

It is an arithmetic number, because the mean of its divisors is an integer number (21168).

2⁶⁴⁴⁰²⁸ is an apocalyptic number.

644028 is a gapful number since it is divisible by the number (68) 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 644028, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1016064).

644028 is an abundant number, since it is smaller than the sum of its proper divisors (1388100).

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

644028 is a wasteful number, since it uses less digits than its factorization.

644028 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 83 (or 81 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 24.

The square root of 644028 is about 802.5135512875. The cubic root of 644028 is about 86.3578026111.

The spelling of 644028 in words is "six hundred forty-four thousand, twenty-eight".