21212020021 has 2 divisors, whose sum is σ = 21212020022. Its totient is φ = 21212020020.

The previous prime is 21212020009. The next prime is 21212020087. The reversal of 21212020021 is 12002021212.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19907799025 + 1304220996 = 141095^2 + 36114^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212020021 - 2¹⁵ = 21211987253 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21212019983 and 21212020010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21212020001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10606010010 + 10606010011.

It is an arithmetic number, because the mean of its divisors is an integer number (10606010011).

Almost surely, 2^21212020021 is an apocalyptic number.

It is an amenable number.

21212020021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21212020021 is an equidigital number, since it uses as much as digits as its factorization.

21212020021 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 13.

Adding to 21212020021 its reverse (12002021212), we get a palindrome (33214041233).

The spelling of 21212020021 in words is "twenty-one billion, two hundred twelve million, twenty thousand, twenty-one".