21120020021 has 4 divisors (see below), whose sum is σ = 21137290272. Its totient is φ = 21102749772.

The previous prime is 21120019961. The next prime is 21120020029. The reversal of 21120020021 is 12002002112.

It is a happy number.

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 21120020021 - 2²⁶ = 21052911157 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21120019984 and 21120020011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21120020029) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8633291 + ... + 8635736.

It is an arithmetic number, because the mean of its divisors is an integer number (5284322568).

Almost surely, 2^21120020021 is an apocalyptic number.

It is an amenable number.

21120020021 is a deficient number, since it is larger than the sum of its proper divisors (17270251).

21120020021 is a wasteful number, since it uses less digits than its factorization.

21120020021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17270250.

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21120020021 its reverse (12002002112), we get a palindrome (33122022133).

The spelling of 21120020021 in words is "twenty-one billion, one hundred twenty million, twenty thousand, twenty-one".