668681 has 4 divisors (see below), whose sum is σ = 720132. Its totient is φ = 617232.

The previous prime is 668677. The next prime is 668687. The reversal of 668681 is 186866.

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

It can be written as a sum of positive squares in 2 ways, for example, as 409600 + 259081 = 640^2 + 509^2 .

It is a cyclic number.

It is not a de Polignac number, because 668681 - 2² = 668677 is a prime.

It is a super-2 number, since 2×668681² = 894268559522, which contains 22 as substring.

It is an Ulam number.

It is a Duffinian number.

It is a Curzon number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 668681.

It is not an unprimeable number, because it can be changed into a prime (668687) 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, 25706 + ... + 25731.

It is an arithmetic number, because the mean of its divisors is an integer number (180033).

2⁶⁶⁸⁶⁸¹ is an apocalyptic number.

It is an amenable number.

668681 is a deficient number, since it is larger than the sum of its proper divisors (51451).

668681 is a wasteful number, since it uses less digits than its factorization.

668681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51450.

The product of its digits is 13824, while the sum is 35.

The square root of 668681 is about 817.7291727705. The cubic root of 668681 is about 87.4459421199.

The spelling of 668681 in words is "six hundred sixty-eight thousand, six hundred eighty-one".