21011020021 has 16 divisors (see below), whose sum is σ = 22337281600. Its totient is φ = 19707712128.

The previous prime is 21011019973. The next prime is 21011020061. The reversal of 21011020021 is 12002011012.

It is a cyclic number.

It is not a de Polignac number, because 21011020021 - 2⁹ = 21011019509 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21011020061) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 831745 + ... + 856633.

It is an arithmetic number, because the mean of its divisors is an integer number (1396080100).

Almost surely, 2^21011020021 is an apocalyptic number.

It is an amenable number.

21011020021 is a deficient number, since it is larger than the sum of its proper divisors (1326261579).

21011020021 is a wasteful number, since it uses less digits than its factorization.

21011020021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25348.

The product of its (nonzero) digits is 8, while the sum is 10.

Adding to 21011020021 its reverse (12002011012), we get a palindrome (33013031033).

Subtracting from 21011020021 its reverse (12002011012), we obtain a palindrome (9009009009).

The spelling of 21011020021 in words is "twenty-one billion, eleven million, twenty thousand, twenty-one".