687681 has 12 divisors (see below), whose sum is σ = 1003860. Its totient is φ = 453600.

The previous prime is 687679. The next prime is 687683. The reversal of 687681 is 186786.

687681 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is an interprime number because it is at equal distance from previous prime (687679) and next prime (687683).

It can be written as a sum of positive squares in 2 ways, for example, as 540225 + 147456 = 735^2 + 384^2 .

It is not a de Polignac number, because 687681 - 2¹ = 687679 is a prime.

It is a super-2 number, since 2×687681² = 945810315522, which contains 22 as substring.

687681 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (687683) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 631 + ... + 1331.

It is an arithmetic number, because the mean of its divisors is an integer number (83655).

2⁶⁸⁷⁶⁸¹ is an apocalyptic number.

It is an amenable number.

687681 is a deficient number, since it is larger than the sum of its proper divisors (316179).

687681 is a wasteful number, since it uses less digits than its factorization.

687681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 816 (or 813 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 687681 is about 829.2653375127. The cubic root of 687681 is about 88.2664530738.

The spelling of 687681 in words is "six hundred eighty-seven thousand, six hundred eighty-one".