640900 has 72 divisors (see below), whose sum is σ = 1640520. Its totient is φ = 215040.

The previous prime is 640891. The next prime is 640901. The reversal of 640900 is 9046.

It is a happy number.

It can be written as a sum of positive squares in 12 ways, for example, as 186624 + 454276 = 432^2 + 674^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640901) by changing a digit.

640900 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 23 ways as a sum of consecutive naturals, for example, 22086 + ... + 22114.

It is an arithmetic number, because the mean of its divisors is an integer number (22785).

2⁶⁴⁰⁹⁰⁰ 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 640900, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (820260).

640900 is an abundant number, since it is smaller than the sum of its proper divisors (999620).

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

640900 is a wasteful number, since it uses less digits than its factorization.

640900 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73 (or 66 counting only the distinct ones).

The product of its (nonzero) digits is 216, while the sum is 19.

The square root of 640900 is about 800.5623023850. The cubic root of 640900 is about 86.2177643310.

Adding to 640900 its reverse (9046), we get a palindrome (649946).

It can be divided in two parts, 640 and 900, that added together give a triangular number (1540 = T₅₅).

The spelling of 640900 in words is "six hundred forty thousand, nine hundred".