21020001021 has 12 divisors (see below), whose sum is σ = 30432349948. Its totient is φ = 13980968064.

The previous prime is 21020000927. The next prime is 21020001071. The reversal of 21020001021 is 12010002012.

It can be written as a sum of positive squares in 2 ways, for example, as 13625892900 + 7394108121 = 116730^2 + 85989^2 .

It is not a de Polignac number, because 21020001021 - 2¹⁴ = 21019984637 is a prime.

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

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21020000994 and 21020001012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020001071) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2693050 + ... + 2700843.

Almost surely, 2^21020001021 is an apocalyptic number.

It is an amenable number.

21020001021 is a deficient number, since it is larger than the sum of its proper divisors (9412348927).

21020001021 is a wasteful number, since it uses less digits than its factorization.

21020001021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5394332 (or 5394329 counting only the distinct ones).

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

Adding to 21020001021 its reverse (12010002012), we get a palindrome (33030003033).

Subtracting from 21020001021 its reverse (12010002012), we obtain a palindrome (9009999009).

The spelling of 21020001021 in words is "twenty-one billion, twenty million, one thousand, twenty-one".