21123221 has 4 divisors (see below), whose sum is σ = 24140832. Its totient is φ = 18105612.

The previous prime is 21123211. The next prime is 21123287. The reversal of 21123221 is 12232112.

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 not a de Polignac number, because 21123221 - 2¹⁰ = 21122197 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21123196 and 21123205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21123211) 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, 1508795 + ... + 1508808.

It is an arithmetic number, because the mean of its divisors is an integer number (6035208).

Almost surely, 2^21123221 is an apocalyptic number.

It is an amenable number.

21123221 is a deficient number, since it is larger than the sum of its proper divisors (3017611).

21123221 is an equidigital number, since it uses as much as digits as its factorization.

21123221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3017610.

The product of its digits is 48, while the sum is 14.

The square root of 21123221 is about 4596.0005439512. Note that the first 3 decimals coincide. The cubic root of 21123221 is about 276.4309805526.

Adding to 21123221 its reverse (12232112), we get a palindrome (33355333).

It can be divided in two parts, 211 and 23221, that added together give a palindrome (23432).

The spelling of 21123221 in words is "twenty-one million, one hundred twenty-three thousand, two hundred twenty-one".