21001220210021 has 2 divisors, whose sum is σ = 21001220210022. Its totient is φ = 21001220210020.

The previous prime is 21001220210017. The next prime is 21001220210027. The reversal of 21001220210021 is 12001202210012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17524990473796 + 3476229736225 = 4186286^2 + 1864465^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001220210021 - 2² = 21001220210017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21001220209978 and 21001220210005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001220210027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500610105010 + 10500610105011.

It is an arithmetic number, because the mean of its divisors is an integer number (10500610105011).

Almost surely, 2^{21001220210021} is an apocalyptic number.

It is an amenable number.

21001220210021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001220210021 is an equidigital number, since it uses as much as digits as its factorization.

21001220210021 is an odious number, because the sum of its binary digits is odd.

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

Adding to 21001220210021 its reverse (12001202210012), we get a palindrome (33002422420033).

Subtracting from 21001220210021 its reverse (12001202210012), we obtain a square (9000018000009 = 3000003²).

The spelling of 21001220210021 in words is "twenty-one trillion, one billion, two hundred twenty million, two hundred ten thousand, twenty-one".