640440 has 64 divisors (see below), whose sum is σ = 2138400. Its totient is φ = 170496.

The previous prime is 640421. The next prime is 640457. The reversal of 640440 is 44046.

640440 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

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 640440.

It is an unprimeable number.

640440 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 15 ways as a sum of consecutive naturals, for example, 784 + ... + 1376.

2⁶⁴⁰⁴⁴⁰ is an apocalyptic number.

640440 is a gapful number since it is divisible by the number (60) 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 640440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1069200).

640440 is an abundant number, since it is smaller than the sum of its proper divisors (1497960).

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

640440 is a wasteful number, since it uses less digits than its factorization.

640440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 613 (or 603 counting only the distinct ones).

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

The square root of 640440 is about 800.2749527506. The cubic root of 640440 is about 86.1971320619.

Adding to 640440 its reverse (44046), we get a palindrome (684486).

The spelling of 640440 in words is "six hundred forty thousand, four hundred forty".