688721 has 16 divisors (see below), whose sum is σ = 829440. Its totient is φ = 564480.

The previous prime is 688717. The next prime is 688729. The reversal of 688721 is 127886.

It is a cyclic number.

It is not a de Polignac number, because 688721 - 2² = 688717 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 688721.

It is not an unprimeable number, because it can be changed into a prime (688729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 5360 + ... + 5486.

It is an arithmetic number, because the mean of its divisors is an integer number (51840).

2⁶⁸⁸⁷²¹ is an apocalyptic number.

It is an amenable number.

688721 is a deficient number, since it is larger than the sum of its proper divisors (140719).

688721 is a wasteful number, since it uses less digits than its factorization.

688721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 184.

The product of its digits is 5376, while the sum is 32.

The square root of 688721 is about 829.8921616692. The cubic root of 688721 is about 88.3109266375.

The spelling of 688721 in words is "six hundred eighty-eight thousand, seven hundred twenty-one".