21030221 has 4 divisors (see below), whose sum is σ = 21040572. Its totient is φ = 21019872.

The previous prime is 21030203. The next prime is 21030227. The reversal of 21030221 is 12203012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 14212900 + 6817321 = 3770^2 + 2611^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21030221 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 (21030227) 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, 1010 + ... + 6563.

It is an arithmetic number, because the mean of its divisors is an integer number (5260143).

Almost surely, 2^21030221 is an apocalyptic number.

It is an amenable number.

21030221 is a deficient number, since it is larger than the sum of its proper divisors (10351).

21030221 is an equidigital number, since it uses as much as digits as its factorization.

21030221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10350.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21030221 is about 4585.8718909276. The cubic root of 21030221 is about 276.0246993579.

Adding to 21030221 its reverse (12203012), we get a palindrome (33233233).

The spelling of 21030221 in words is "twenty-one million, thirty thousand, two hundred twenty-one".