21002120120021 has 6 divisors (see below), whose sum is σ = 22165672481622. Its totient is φ = 19896745376520.

The previous prime is 21002120119991. The next prime is 21002120120083. The reversal of 21002120120021 is 12002102120012.

It can be written as a sum of positive squares in only one way, i.e., 16429151717521 + 4572968402500 = 4053289^2 + 2138450^2 .

It is not a de Polignac number, because 21002120120021 - 2¹⁸ = 21002119857877 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21002120119978 and 21002120120005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21002120140021) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 29088808670 + ... + 29088809391.

It is an arithmetic number, because the mean of its divisors is an integer number (3694278746937).

Almost surely, 2^{21002120120021} is an apocalyptic number.

It is an amenable number.

21002120120021 is a deficient number, since it is larger than the sum of its proper divisors (1163552361601).

21002120120021 is an equidigital number, since it uses as much as digits as its factorization.

21002120120021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 58177618099 (or 58177618080 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 14.

Adding to 21002120120021 its reverse (12002102120012), we get a palindrome (33004222240033).

Subtracting from 21002120120021 its reverse (12002102120012), we obtain a square (9000018000009 = 3000003²).

The spelling of 21002120120021 in words is "twenty-one trillion, two billion, one hundred twenty million, one hundred twenty thousand, twenty-one".