21212210021 has 4 divisors (see below), whose sum is σ = 21319886412. Its totient is φ = 21104533632.

The previous prime is 21212209951. The next prime is 21212210059. The reversal of 21212210021 is 12001221212.

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 20206622500 + 1005587521 = 142150^2 + 31711^2 .

It is a cyclic number.

It is not a de Polignac number, because 21212210021 - 2³⁰ = 20138468197 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21212209978 and 21212210005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21212210081) 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, 53837900 + ... + 53838293.

It is an arithmetic number, because the mean of its divisors is an integer number (5329971603).

Almost surely, 2^21212210021 is an apocalyptic number.

It is an amenable number.

21212210021 is a deficient number, since it is larger than the sum of its proper divisors (107676391).

21212210021 is a wasteful number, since it uses less digits than its factorization.

21212210021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 107676390.

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

Adding to 21212210021 its reverse (12001221212), we get a palindrome (33213431233).

The spelling of 21212210021 in words is "twenty-one billion, two hundred twelve million, two hundred ten thousand, twenty-one".