668891 has 4 divisors (see below), whose sum is σ = 678384. Its totient is φ = 659400.

The previous prime is 668879. The next prime is 668903. The reversal of 668891 is 198866.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (668879) and next prime (668903).

It is a cyclic number.

It is not a de Polignac number, because 668891 - 2¹⁰ = 667867 is a prime.

It is an Ulam number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668821) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4640 + ... + 4781.

It is an arithmetic number, because the mean of its divisors is an integer number (169596).

2⁶⁶⁸⁸⁹¹ is an apocalyptic number.

668891 is a deficient number, since it is larger than the sum of its proper divisors (9493).

668891 is an equidigital number, since it uses as much as digits as its factorization.

668891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9492.

The product of its digits is 20736, while the sum is 38.

The square root of 668891 is about 817.8575670616. The cubic root of 668891 is about 87.4550953264.

The spelling of 668891 in words is "six hundred sixty-eight thousand, eight hundred ninety-one".