666861 has 8 divisors (see below), whose sum is σ = 957600. Its totient is φ = 410352.

The previous prime is 666857. The next prime is 666871. The reversal of 666861 is 168666.

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

It is not a de Polignac number, because 666861 - 2² = 666857 is a prime.

It is a Smith number, since the sum of its digits (33) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

666861 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (666811) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 8511 + ... + 8588.

It is an arithmetic number, because the mean of its divisors is an integer number (119700).

2⁶⁶⁶⁸⁶¹ is an apocalyptic number.

It is an amenable number.

666861 is a deficient number, since it is larger than the sum of its proper divisors (290739).

666861 is a wasteful number, since it uses less digits than its factorization.

666861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17115.

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

The square root of 666861 is about 816.6155766332. The cubic root of 666861 is about 87.3665339392.

The spelling of 666861 in words is "six hundred sixty-six thousand, eight hundred sixty-one".