668991 has 8 divisors (see below), whose sum is σ = 897840. Its totient is φ = 443072.

The previous prime is 668989. The next prime is 668999. The reversal of 668991 is 199866.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 668991 - 2¹ = 668989 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668999) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 126 + ... + 1163.

It is an arithmetic number, because the mean of its divisors is an integer number (112230).

2⁶⁶⁸⁹⁹¹ is an apocalyptic number.

668991 is a deficient number, since it is larger than the sum of its proper divisors (228849).

668991 is a wasteful number, since it uses less digits than its factorization.

668991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1465.

The product of its digits is 23328, while the sum is 39.

The square root of 668991 is about 817.9187001163. The cubic root of 668991 is about 87.4594533228.

The spelling of 668991 in words is "six hundred sixty-eight thousand, nine hundred ninety-one".