16840021 has 4 divisors (see below), whose sum is σ = 18370944. Its totient is φ = 15309100.

The previous prime is 16840009. The next prime is 16840067. The reversal of 16840021 is 12004861.

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 16840021 - 2⁹ = 16839509 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 16839974 and 16840001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16840321) 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, 765445 + ... + 765466.

It is an arithmetic number, because the mean of its divisors is an integer number (4592736).

Almost surely, 2^16840021 is an apocalyptic number.

16840021 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

16840021 is a deficient number, since it is larger than the sum of its proper divisors (1530923).

16840021 is a wasteful number, since it uses less digits than its factorization.

16840021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1530922.

The product of its (nonzero) digits is 384, while the sum is 22.

The square root of 16840021 is about 4103.6594644293. The cubic root of 16840021 is about 256.3190449679.

Adding to 16840021 its reverse (12004861), we get a palindrome (28844882).

The spelling of 16840021 in words is "sixteen million, eight hundred forty thousand, twenty-one".