640640 has 128 divisors (see below), whose sum is σ = 2056320. Its totient is φ = 184320.

The previous prime is 640631. The next prime is 640649. The reversal of 640640 is 46046.

It is an interprime number because it is at equal distance from previous prime (640631) and next prime (640649).

It is a tau number, because it is divible by the number of its divisors (128).

It is a hoax number, since the sum of its digits (20) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640649) by changing a digit.

640640 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 49274 + ... + 49286.

It is an arithmetic number, because the mean of its divisors is an integer number (16065).

2⁶⁴⁰⁶⁴⁰ 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 640640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1028160).

640640 is an abundant number, since it is smaller than the sum of its proper divisors (1415680).

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

640640 is a wasteful number, since it uses less digits than its factorization.

640640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 50 (or 38 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 20.

The square root of 640640 is about 800.3999000500. The cubic root of 640640 is about 86.2061038272.

Adding to 640640 its reverse (46046), we get a palindrome (686686).

It can be divided in two parts, 6406 and 40, that added together give a palindrome (6446).

The spelling of 640640 in words is "six hundred forty thousand, six hundred forty".