666891 has 6 divisors (see below), whose sum is σ = 963300. Its totient is φ = 444588.

The previous prime is 666889. The next prime is 666901. The reversal of 666891 is 198666.

It is not a de Polignac number, because 666891 - 2¹ = 666889 is a prime.

It is not an unprimeable number, because it can be changed into a prime (666811) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 37041 + ... + 37058.

It is an arithmetic number, because the mean of its divisors is an integer number (160550).

2⁶⁶⁶⁸⁹¹ is an apocalyptic number.

666891 is a deficient number, since it is larger than the sum of its proper divisors (296409).

666891 is a wasteful number, since it uses less digits than its factorization.

666891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 74105 (or 74102 counting only the distinct ones).

The product of its digits is 15552, while the sum is 36.

The square root of 666891 is about 816.6339449227. The cubic root of 666891 is about 87.3678440356.

The spelling of 666891 in words is "six hundred sixty-six thousand, eight hundred ninety-one".