681 has 4 divisors (see below), whose sum is σ = 912. Its totient is φ = 452.

The previous prime is 677. The next prime is 683. The reversal of 681 is 186.

681 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, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 681 - 2² = 677 is a prime.

It is a super-2 number, since 2×681² = 927522, which contains 22 as substring.

It is a D-number.

It is a plaindrome in base 11, base 12 and base 14.

It is a nialpdrome in base 4.

It is a self number, because there is not a number n which added to its sum of digits gives 681.

It is not an unprimeable number, because it can be changed into a prime (683) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 111 + ... + 116.

It is an arithmetic number, because the mean of its divisors is an integer number (228).

681 is the 17-th centered pentagonal number.

It is an amenable number.

681 is a deficient number, since it is larger than the sum of its proper divisors (231).

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

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

The sum of its prime factors is 230.

The product of its digits is 48, while the sum is 15.

The square root of 681 is about 26.0959767014. The cubic root of 681 is about 8.7979678503.

Adding to 681 its sum of digits (15), we get a palindrome (696).

Subtracting from 681 its sum of digits (15), we obtain a palindrome (666).

Adding to 681 its product of digits (48), we get a 6-th power (729 = 3⁶).

The spelling of 681 in words is "six hundred eighty-one", and thus it is an aban number.