21002110021 has 4 divisors (see below), whose sum is σ = 21068363052. Its totient is φ = 20935856992.

The previous prime is 21002110007. The next prime is 21002110027. The reversal of 21002110021 is 12001120012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1688059396 + 19314050625 = 41086^2 + 138975^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002110021 - 2¹³ = 21002101829 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002110027) 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, 33126040 + ... + 33126673.

It is an arithmetic number, because the mean of its divisors is an integer number (5267090763).

Almost surely, 2^21002110021 is an apocalyptic number.

It is an amenable number.

21002110021 is a deficient number, since it is larger than the sum of its proper divisors (66253031).

21002110021 is an equidigital number, since it uses as much as digits as its factorization.

21002110021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66253030.

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

Adding to 21002110021 its reverse (12001120012), we get a palindrome (33003230033).

Subtracting from 21002110021 its reverse (12001120012), we obtain a palindrome (9000990009).

The spelling of 21002110021 in words is "twenty-one billion, two million, one hundred ten thousand, twenty-one".