21012122221 has 4 divisors (see below), whose sum is σ = 21019303872. Its totient is φ = 21004940572.

The previous prime is 21012122191. The next prime is 21012122227. The reversal of 21012122221 is 12222121012.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21012122221 - 2¹⁵ = 21012089453 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21012122195 and 21012122204.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21012122227) 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, 3586435 + ... + 3592288.

It is an arithmetic number, because the mean of its divisors is an integer number (5254825968).

Almost surely, 2^21012122221 is an apocalyptic number.

It is an amenable number.

21012122221 is a deficient number, since it is larger than the sum of its proper divisors (7181651).

21012122221 is an equidigital number, since it uses as much as digits as its factorization.

21012122221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7181650.

The product of its (nonzero) digits is 64, while the sum is 16.

Adding to 21012122221 its reverse (12222121012), we get a palindrome (33234243233).

The spelling of 21012122221 in words is "twenty-one billion, twelve million, one hundred twenty-two thousand, two hundred twenty-one".