640668 has 48 divisors (see below), whose sum is σ = 1774080. Its totient is φ = 176064.

The previous prime is 640667. The next prime is 640669. The reversal of 640668 is 866046.

It is a happy number.

640668 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

640668 is an esthetic number in base 8, because in such base its adjacent digits differ by 1.

It is an interprime number because it is at equal distance from previous prime (640667) and next prime (640669).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (640663) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2305 + ... + 2567.

It is an arithmetic number, because the mean of its divisors is an integer number (36960).

2⁶⁴⁰⁶⁶⁸ 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 640668, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (887040).

640668 is an abundant number, since it is smaller than the sum of its proper divisors (1133412).

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

640668 is a wasteful number, since it uses less digits than its factorization.

640668 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 306 (or 304 counting only the distinct ones).

The product of its (nonzero) digits is 6912, while the sum is 30.

The square root of 640668 is about 800.4173911154. The cubic root of 640668 is about 86.2073597253.

The spelling of 640668 in words is "six hundred forty thousand, six hundred sixty-eight".