666689 has 4 divisors (see below), whose sum is σ = 705924. Its totient is φ = 627456.

The previous prime is 666683. The next prime is 666697. The reversal of 666689 is 986666.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 986666 = 2 ⋅493333.

It can be written as a sum of positive squares in 2 ways, for example, as 297025 + 369664 = 545^2 + 608^2 .

It is a cyclic number.

It is not a de Polignac number, because 666689 - 2⁸ = 666433 is a prime.

It is a Duffinian number.

It is a plaindrome in base 10.

It is not an unprimeable number, because it can be changed into a prime (666683) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19592 + ... + 19625.

It is an arithmetic number, because the mean of its divisors is an integer number (176481).

2⁶⁶⁶⁶⁸⁹ is an apocalyptic number.

It is an amenable number.

666689 is a deficient number, since it is larger than the sum of its proper divisors (39235).

666689 is a wasteful number, since it uses less digits than its factorization.

666689 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 39234.

The product of its digits is 93312, while the sum is 41.

The square root of 666689 is about 816.5102571309. The cubic root of 666689 is about 87.3590219609.

The spelling of 666689 in words is "six hundred sixty-six thousand, six hundred eighty-nine".