640866 has 32 divisors (see below), whose sum is σ = 1392768. Its totient is φ = 195840.

The previous prime is 640859. The next prime is 640873. The reversal of 640866 is 668046.

It is a happy number.

640866 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (640859) and next prime (640873).

It is an unprimeable number.

640866 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, 6171 + ... + 6273.

It is an arithmetic number, because the mean of its divisors is an integer number (43524).

2⁶⁴⁰⁸⁶⁶ is an apocalyptic number.

640866 is an abundant number, since it is smaller than the sum of its proper divisors (751902).

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

640866 is a wasteful number, since it uses less digits than its factorization.

640866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 186.

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

The square root of 640866 is about 800.5410670290. The cubic root of 640866 is about 86.2162396752.

The spelling of 640866 in words is "six hundred forty thousand, eight hundred sixty-six".