640920 has 96 divisors (see below), whose sum is σ = 2257200. Its totient is φ = 145152.

The previous prime is 640919. The next prime is 640933. The reversal of 640920 is 29046.

640920 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 (21).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5826 + ... + 5934.

2⁶⁴⁰⁹²⁰ is an apocalyptic number.

640920 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 640920, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1128600).

640920 is an abundant number, since it is smaller than the sum of its proper divisors (1616280).

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

640920 is a wasteful number, since it uses less digits than its factorization.

640920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 137 (or 126 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 21.

The square root of 640920 is about 800.5747935078. The cubic root of 640920 is about 86.2186611622.

Adding to 640920 its reverse (29046), we get a palindrome (669966).

The spelling of 640920 in words is "six hundred forty thousand, nine hundred twenty".