666391 has 8 divisors (see below), whose sum is σ = 752400. Its totient is φ = 584640.

The previous prime is 666353. The next prime is 666403. The reversal of 666391 is 193666.

666391 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It is not a de Polignac number, because 666391 - 2¹³ = 658199 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666301) 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, 726 + ... + 1363.

It is an arithmetic number, because the mean of its divisors is an integer number (94050).

2⁶⁶⁶³⁹¹ is an apocalyptic number.

666391 is a deficient number, since it is larger than the sum of its proper divisors (86009).

666391 is a wasteful number, since it uses less digits than its factorization.

666391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2129.

The product of its digits is 5832, while the sum is 31.

The square root of 666391 is about 816.3277528052. The cubic root of 666391 is about 87.3460039629.

The spelling of 666391 in words is "six hundred sixty-six thousand, three hundred ninety-one".