21002020021 has 8 divisors (see below), whose sum is σ = 21274141824. Its totient is φ = 20731210320.

The previous prime is 21002019959. The next prime is 21002020043. The reversal of 21002020021 is 12002020012.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21002020021 - 2²³ = 20993631413 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 (21002020051) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 295786 + ... + 359851.

It is an arithmetic number, because the mean of its divisors is an integer number (2659267728).

Almost surely, 2^21002020021 is an apocalyptic number.

It is an amenable number.

21002020021 is a deficient number, since it is larger than the sum of its proper divisors (272121803).

21002020021 is a wasteful number, since it uses less digits than its factorization.

21002020021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 656051.

The product of its (nonzero) digits is 16, while the sum is 10.

Adding to 21002020021 its reverse (12002020012), we get a palindrome (33004040033).

Subtracting from 21002020021 its reverse (12002020012), we obtain a palindrome (9000000009).

The spelling of 21002020021 in words is "twenty-one billion, two million, twenty thousand, twenty-one".