688021 has 8 divisors (see below), whose sum is σ = 716184. Its totient is φ = 660480.

The previous prime is 688013. The next prime is 688027. The reversal of 688021 is 120886.

688021 = 109² + 110² + ... + 149².

It can be written as a sum of positive squares in 4 ways, for example, as 70225 + 617796 = 265^2 + 786^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 688021 - 2³ = 688013 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (688027) 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 7 ways as a sum of consecutive naturals, for example, 3891 + ... + 4063.

It is an arithmetic number, because the mean of its divisors is an integer number (89523).

2⁶⁸⁸⁰²¹ is an apocalyptic number.

It is an amenable number.

688021 is a deficient number, since it is larger than the sum of its proper divisors (28163).

688021 is a wasteful number, since it uses less digits than its factorization.

688021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 311.

The product of its (nonzero) digits is 768, while the sum is 25.

The square root of 688021 is about 829.4703129106. The cubic root of 688021 is about 88.2809974384.

The spelling of 688021 in words is "six hundred eighty-eight thousand, twenty-one".