21010020021 has 24 divisors (see below), whose sum is σ = 31451890080. Its totient is φ = 13498875936.

The previous prime is 21010020007. The next prime is 21010020047. The reversal of 21010020021 is 12002001012.

It is not a de Polignac number, because 21010020021 - 2⁶ = 21010019957 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21010019985 and 21010020012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21010020071) 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 23 ways as a sum of consecutive naturals, for example, 69186 + ... + 216348.

It is an arithmetic number, because the mean of its divisors is an integer number (1310495420).

Almost surely, 2^21010020021 is an apocalyptic number.

It is an amenable number.

21010020021 is a deficient number, since it is larger than the sum of its proper divisors (10441870059).

21010020021 is a wasteful number, since it uses less digits than its factorization.

21010020021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 147745 (or 147742 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

Adding to 21010020021 its reverse (12002001012), we get a palindrome (33012021033).

The spelling of 21010020021 in words is "twenty-one billion, ten million, twenty thousand, twenty-one".