640044 has 36 divisors (see below), whose sum is σ = 1690416. Its totient is φ = 203808.

The previous prime is 640043. The next prime is 640049. The reversal of 640044 is 440046.

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a nialpdrome in base 15.

It is a junction number, because it is equal to n+sod(n) for n = 639999 and 640026.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 640044.

It is not an unprimeable number, because it can be changed into a prime (640043) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 442 + ... + 1214.

It is an arithmetic number, because the mean of its divisors is an integer number (46956).

2⁶⁴⁰⁰⁴⁴ 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 640044, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (845208).

640044 is an abundant number, since it is smaller than the sum of its proper divisors (1050372).

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

640044 is a wasteful number, since it uses less digits than its factorization.

640044 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 806 (or 801 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 18.

The square root of 640044 is about 800.0274995274. The cubic root of 640044 is about 86.1793624545.

The spelling of 640044 in words is "six hundred forty thousand, forty-four".