21244221 has 8 divisors (see below), whose sum is σ = 31472960. Its totient is φ = 14162796.

The previous prime is 21244219. The next prime is 21244229. The reversal of 21244221 is 12244212.

It is not a de Polignac number, because 21244221 - 2¹ = 21244219 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21244194 and 21244203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21244229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 393385 + ... + 393438.

It is an arithmetic number, because the mean of its divisors is an integer number (3934120).

It is a self-describing number.

Almost surely, 2^21244221 is an apocalyptic number.

It is an amenable number.

21244221 is a deficient number, since it is larger than the sum of its proper divisors (10228739).

21244221 is an equidigital number, since it uses as much as digits as its factorization.

21244221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 786832 (or 786826 counting only the distinct ones).

The product of its digits is 256, while the sum is 18.

The square root of 21244221 is about 4609.1453654664. The cubic root of 21244221 is about 276.9578017886.

Adding to 21244221 its reverse (12244212), we get a palindrome (33488433).

Subtracting from 21244221 its reverse (12244212), we obtain a palindrome (9000009).

The spelling of 21244221 in words is "twenty-one million, two hundred forty-four thousand, two hundred twenty-one".