685981 has 4 divisors (see below), whose sum is σ = 695452. Its totient is φ = 676512.

The previous prime is 685973. The next prime is 685987. The reversal of 685981 is 189586.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 189586 = 2 ⋅94793.

It can be written as a sum of positive squares in 2 ways, for example, as 136900 + 549081 = 370^2 + 741^2 .

It is a cyclic number.

It is not a de Polignac number, because 685981 - 2³ = 685973 is a prime.

It is a super-2 number, since 2×685981² = 941139864722, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 685981.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (685987) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4626 + ... + 4771.

It is an arithmetic number, because the mean of its divisors is an integer number (173863).

2⁶⁸⁵⁹⁸¹ is an apocalyptic number.

It is an amenable number.

685981 is a deficient number, since it is larger than the sum of its proper divisors (9471).

685981 is an equidigital number, since it uses as much as digits as its factorization.

685981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9470.

The product of its digits is 17280, while the sum is 37.

The square root of 685981 is about 828.2396996039. The cubic root of 685981 is about 88.1936592504.

The spelling of 685981 in words is "six hundred eighty-five thousand, nine hundred eighty-one".