21202220021 has 4 divisors (see below), whose sum is σ = 22449409452. Its totient is φ = 19955030592.

The previous prime is 21202220009. The next prime is 21202220047. The reversal of 21202220021 is 12002220212.

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 18773110225 + 2429109796 = 137015^2 + 49286^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21202220021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21202219978 and 21202220005.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21202222021) 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, 623594690 + ... + 623594723.

It is an arithmetic number, because the mean of its divisors is an integer number (5612352363).

Almost surely, 2^21202220021 is an apocalyptic number.

It is an amenable number.

21202220021 is a deficient number, since it is larger than the sum of its proper divisors (1247189431).

21202220021 is a wasteful number, since it uses less digits than its factorization.

21202220021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1247189430.

The product of its (nonzero) digits is 64, while the sum is 14.

Adding to 21202220021 its reverse (12002220212), we get a palindrome (33204440233).

The spelling of 21202220021 in words is "twenty-one billion, two hundred two million, two hundred twenty thousand, twenty-one".