685666 has 4 divisors (see below), whose sum is σ = 1028502. Its totient is φ = 342832.

The previous prime is 685649. The next prime is 685669. The reversal of 685666 is 666586.

685666 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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

It can be written as a sum of positive squares in only one way, i.e., 680625 + 5041 = 825^2 + 71^2 .

It is a nialpdrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (685669) by changing a digit.

685666 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 171415 + ... + 171418.

2⁶⁸⁵⁶⁶⁶ is an apocalyptic number.

685666 is a deficient number, since it is larger than the sum of its proper divisors (342836).

685666 is a wasteful number, since it uses less digits than its factorization.

685666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 342835.

The product of its digits is 51840, while the sum is 37.

The square root of 685666 is about 828.0495154277. The cubic root of 685666 is about 88.1801577802.

The spelling of 685666 in words is "six hundred eighty-five thousand, six hundred sixty-six".