21120204221 has 4 divisors (see below), whose sum is σ = 21139458012. Its totient is φ = 21100950432.

The previous prime is 21120204211. The next prime is 21120204239. The reversal of 21120204221 is 12240202112.

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 6969912196 + 14150292025 = 83486^2 + 118955^2 .

It is a cyclic number.

It is not a de Polignac number, because 21120204221 - 2¹⁰ = 21120203197 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21120204221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21120204211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 9625250 + ... + 9627443.

It is an arithmetic number, because the mean of its divisors is an integer number (5284864503).

Almost surely, 2^21120204221 is an apocalyptic number.

It is an amenable number.

21120204221 is a deficient number, since it is larger than the sum of its proper divisors (19253791).

21120204221 is a wasteful number, since it uses less digits than its factorization.

21120204221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19253790.

The product of its (nonzero) digits is 128, while the sum is 17.

Adding to 21120204221 its reverse (12240202112), we get a palindrome (33360406333).

The spelling of 21120204221 in words is "twenty-one billion, one hundred twenty million, two hundred four thousand, two hundred twenty-one".