21000122221 has 4 divisors (see below), whose sum is σ = 22615516252. Its totient is φ = 19384728192.

The previous prime is 21000122201. The next prime is 21000122233. The reversal of 21000122221 is 12222100012.

It is a happy number.

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 8338246596 + 12661875625 = 91314^2 + 112525^2 .

It is a cyclic number.

It is not a de Polignac number, because 21000122221 - 2⁷ = 21000122093 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13), and also a Moran number because the ratio is a prime number: 1615394017 = 21000122221 / (2 + 1 + 0 + 0 + 0 + 1 + 2 + 2 + 2 + 2 + 1).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000122201) 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, 807696996 + ... + 807697021.

It is an arithmetic number, because the mean of its divisors is an integer number (5653879063).

Almost surely, 2^21000122221 is an apocalyptic number.

It is an amenable number.

21000122221 is a deficient number, since it is larger than the sum of its proper divisors (1615394031).

21000122221 is a wasteful number, since it uses less digits than its factorization.

21000122221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1615394030.

The product of its (nonzero) digits is 32, while the sum is 13.

Adding to 21000122221 its reverse (12222100012), we get a palindrome (33222222233).

The spelling of 21000122221 in words is "twenty-one billion, one hundred twenty-two thousand, two hundred twenty-one".