643668 has 12 divisors (see below), whose sum is σ = 1501920. Its totient is φ = 214552.

The previous prime is 643661. The next prime is 643681. The reversal of 643668 is 866346.

It is a tau number, because it is divible by the number of its divisors (12).

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 643668.

It is not an unprimeable number, because it can be changed into a prime (643661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 26808 + ... + 26831.

It is an arithmetic number, because the mean of its divisors is an integer number (125160).

2⁶⁴³⁶⁶⁸ is an apocalyptic number.

It is an amenable number.

643668 is an abundant number, since it is smaller than the sum of its proper divisors (858252).

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

643668 is a wasteful number, since it uses less digits than its factorization.

643668 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 53646 (or 53644 counting only the distinct ones).

The product of its digits is 20736, while the sum is 33.

The square root of 643668 is about 802.2892246565. The cubic root of 643668 is about 86.3417087956.

The spelling of 643668 in words is "six hundred forty-three thousand, six hundred sixty-eight".