21021020021 has 4 divisors (see below), whose sum is σ = 21021804000. Its totient is φ = 21020236044.

The previous prime is 21021019997. The next prime is 21021020057. The reversal of 21021020021 is 12002012012.

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 a de Polignac number, because none of the positive numbers 2^k-21021020021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21021019984 and 21021020011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21021020621) 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, 350291 + ... + 405888.

It is an arithmetic number, because the mean of its divisors is an integer number (5255451000).

Almost surely, 2^21021020021 is an apocalyptic number.

It is an amenable number.

21021020021 is a deficient number, since it is larger than the sum of its proper divisors (783979).

21021020021 is an equidigital number, since it uses as much as digits as its factorization.

21021020021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 783978.

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

Adding to 21021020021 its reverse (12002012012), we get a palindrome (33023032033).

The spelling of 21021020021 in words is "twenty-one billion, twenty-one million, twenty thousand, twenty-one".