666491 has 4 divisors (see below), whose sum is σ = 761712. Its totient is φ = 571272.

The previous prime is 666467. The next prime is 666493. The reversal of 666491 is 194666.

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

It is a cyclic number.

It is not a de Polignac number, because 666491 - 2⁶ = 666427 is a prime.

It is not an unprimeable number, because it can be changed into a prime (666493) 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, 47600 + ... + 47613.

It is an arithmetic number, because the mean of its divisors is an integer number (190428).

2⁶⁶⁶⁴⁹¹ is an apocalyptic number.

666491 is a deficient number, since it is larger than the sum of its proper divisors (95221).

666491 is an equidigital number, since it uses as much as digits as its factorization.

666491 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95220.

The product of its digits is 7776, while the sum is 32.

The square root of 666491 is about 816.3890004159. The cubic root of 666491 is about 87.3503728512.

The spelling of 666491 in words is "six hundred sixty-six thousand, four hundred ninety-one".