666681 has 16 divisors (see below), whose sum is σ = 940800. Its totient is φ = 419328.

The previous prime is 666671. The next prime is 666683. The reversal of 666681 is 186666.

It is not a de Polignac number, because 666681 - 2⁵ = 666649 is a prime.

It is a super-2 number, since 2×666681² = 888927111522, which contains 22 as substring.

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

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 6825 + ... + 6921.

It is an arithmetic number, because the mean of its divisors is an integer number (58800).

2⁶⁶⁶⁶⁸¹ is an apocalyptic number.

It is an amenable number.

666681 is a deficient number, since it is larger than the sum of its proper divisors (274119).

666681 is a wasteful number, since it uses less digits than its factorization.

666681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 208.

The product of its digits is 10368, while the sum is 33.

The square root of 666681 is about 816.5053582188. The cubic root of 666681 is about 87.3586725351.

The spelling of 666681 in words is "six hundred sixty-six thousand, six hundred eighty-one".