21312211 has 4 divisors (see below), whose sum is σ = 21322792. Its totient is φ = 21301632.

The previous prime is 21312173. The next prime is 21312223. The reversal of 21312211 is 11221312.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21312211 - 2¹⁵ = 21279443 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21312191 and 21312200.

It is not an unprimeable number, because it can be changed into a prime (21312911) 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, 1230 + ... + 6643.

It is an arithmetic number, because the mean of its divisors is an integer number (5330698).

Almost surely, 2^21312211 is an apocalyptic number.

21312211 is a deficient number, since it is larger than the sum of its proper divisors (10581).

21312211 is an equidigital number, since it uses as much as digits as its factorization.

21312211 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10580.

The product of its digits is 24, while the sum is 13.

The square root of 21312211 is about 4616.5150275939. The cubic root of 21312211 is about 277.2529457144.

Adding to 21312211 its reverse (11221312), we get a palindrome (32533523).

The spelling of 21312211 in words is "twenty-one million, three hundred twelve thousand, two hundred eleven".