666591 has 4 divisors (see below), whose sum is σ = 888792. Its totient is φ = 444392.

The previous prime is 666559. The next prime is 666599. The reversal of 666591 is 195666.

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 666591 - 2⁵ = 666559 is a prime.

It is a super-2 number, since 2×666591² = 888687122562, which contains 22 as substring.

It is a D-number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 666591.

It is not an unprimeable number, because it can be changed into a prime (666599) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111096 + ... + 111101.

It is an arithmetic number, because the mean of its divisors is an integer number (222198).

2⁶⁶⁶⁵⁹¹ is an apocalyptic number.

666591 is a deficient number, since it is larger than the sum of its proper divisors (222201).

666591 is a wasteful number, since it uses less digits than its factorization.

666591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 222200.

The product of its digits is 9720, while the sum is 33.

The square root of 666591 is about 816.4502434319. The cubic root of 666591 is about 87.3547413025.

The spelling of 666591 in words is "six hundred sixty-six thousand, five hundred ninety-one".