21044021 has 4 divisors (see below), whose sum is σ = 21441132. Its totient is φ = 20646912.

The previous prime is 21044003. The next prime is 21044047. The reversal of 21044021 is 12044012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 11464996 + 9579025 = 3386^2 + 3095^2 .

It is a cyclic number.

It is not a de Polignac number, because 21044021 - 2¹⁰ = 21042997 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21043987 and 21044005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21044081) 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, 198476 + ... + 198581.

It is an arithmetic number, because the mean of its divisors is an integer number (5360283).

Almost surely, 2^21044021 is an apocalyptic number.

It is an amenable number.

21044021 is a deficient number, since it is larger than the sum of its proper divisors (397111).

21044021 is an equidigital number, since it uses as much as digits as its factorization.

21044021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 397110.

The product of its (nonzero) digits is 64, while the sum is 14.

The square root of 21044021 is about 4587.3762653613. The cubic root of 21044021 is about 276.0850618234.

Adding to 21044021 its reverse (12044012), we get a palindrome (33088033).

Subtracting from 21044021 its reverse (12044012), we obtain a palindrome (9000009).

The spelling of 21044021 in words is "twenty-one million, forty-four thousand, twenty-one".