21225221 has 4 divisors (see below), whose sum is σ = 21234444. Its totient is φ = 21216000.

The previous prime is 21225209. The next prime is 21225229. The reversal of 21225221 is 12252212.

21225221 is nontrivially palindromic in base 4.

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 can be written as a sum of positive squares in 2 ways, for example, as 15124321 + 6100900 = 3889^2 + 2470^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21225221 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21225221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21225229) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2021 + ... + 6821.

It is an arithmetic number, because the mean of its divisors is an integer number (5308611).

Almost surely, 2^21225221 is an apocalyptic number.

It is an amenable number.

21225221 is a deficient number, since it is larger than the sum of its proper divisors (9223).

21225221 is an equidigital number, since it uses as much as digits as its factorization.

21225221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9222.

The product of its digits is 160, while the sum is 17.

The square root of 21225221 is about 4607.0837847819. The cubic root of 21225221 is about 276.8752104213.

Adding to 21225221 its reverse (12252212), we get a palindrome (33477433).

The spelling of 21225221 in words is "twenty-one million, two hundred twenty-five thousand, two hundred twenty-one".