685681 has 4 divisors (see below), whose sum is σ = 688500. Its totient is φ = 682864.

The previous prime is 685679. The next prime is 685697. The reversal of 685681 is 186586.

It is a happy number.

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 336400 + 349281 = 580^2 + 591^2 .

It is a cyclic number.

It is not a de Polignac number, because 685681 - 2¹ = 685679 is a prime.

It is a super-2 number, since 2×685681² = 940316867522, which contains 22 as substring.

It is a Duffinian number.

685681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (685621) 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 3 ways as a sum of consecutive naturals, for example, 1006 + ... + 1543.

It is an arithmetic number, because the mean of its divisors is an integer number (172125).

2⁶⁸⁵⁶⁸¹ is an apocalyptic number.

It is an amenable number.

685681 is a deficient number, since it is larger than the sum of its proper divisors (2819).

685681 is a wasteful number, since it uses less digits than its factorization.

685681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2818.

The product of its digits is 11520, while the sum is 34.

The square root of 685681 is about 828.0585728075. The cubic root of 685681 is about 88.1808008012.

The spelling of 685681 in words is "six hundred eighty-five thousand, six hundred eighty-one".