1688021 has 4 divisors (see below), whose sum is σ = 1699500. Its totient is φ = 1676544.

The previous prime is 1687999. The next prime is 1688041. The reversal of 1688021 is 1208861.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1208861 = 743 ⋅1627.

It can be written as a sum of positive squares in 2 ways, for example, as 376996 + 1311025 = 614^2 + 1145^2 .

It is a cyclic number.

It is not a de Polignac number, because 1688021 - 2¹⁸ = 1425877 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 (1688041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5516 + ... + 5813.

It is an arithmetic number, because the mean of its divisors is an integer number (424875).

2^1688021 is an apocalyptic number.

It is an amenable number.

1688021 is a deficient number, since it is larger than the sum of its proper divisors (11479).

1688021 is a wasteful number, since it uses less digits than its factorization.

1688021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11478.

The product of its (nonzero) digits is 768, while the sum is 26.

The square root of 1688021 is about 1299.2386231944. The cubic root of 1688021 is about 119.0673300213.

The spelling of 1688021 in words is "one million, six hundred eighty-eight thousand, twenty-one".