21020021021 has 4 divisors (see below), whose sum is σ = 21021001500. Its totient is φ = 21019040544.

The previous prime is 21020021017. The next prime is 21020021023. The reversal of 21020021021 is 12012002012.

It is a happy number.

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 16489384921 + 4530636100 = 128411^2 + 67310^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020021021 - 2² = 21020021017 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21020020993 and 21020021011.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21020021023) 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, 457346 + ... + 501203.

It is an arithmetic number, because the mean of its divisors is an integer number (5255250375).

Almost surely, 2^21020021021 is an apocalyptic number.

It is an amenable number.

21020021021 is a deficient number, since it is larger than the sum of its proper divisors (980479).

21020021021 is an equidigital number, since it uses as much as digits as its factorization.

21020021021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 980478.

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21020021021 its reverse (12012002012), we get a palindrome (33032023033).

The spelling of 21020021021 in words is "twenty-one billion, twenty million, twenty-one thousand, twenty-one".