21201221 has 4 divisors (see below), whose sum is σ = 21548844. Its totient is φ = 20853600.

The previous prime is 21201209. The next prime is 21201251. The reversal of 21201221 is 12210212.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8916196 + 12285025 = 2986^2 + 3505^2 .

It is a cyclic number.

It is not a de Polignac number, because 21201221 - 2⁶ = 21201157 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21201251) 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, 173720 + ... + 173841.

It is an arithmetic number, because the mean of its divisors is an integer number (5387211).

Almost surely, 2^21201221 is an apocalyptic number.

It is an amenable number.

21201221 is a deficient number, since it is larger than the sum of its proper divisors (347623).

21201221 is an equidigital number, since it uses as much as digits as its factorization.

21201221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 347622.

The product of its (nonzero) digits is 16, while the sum is 11.

The square root of 21201221 is about 4604.4783635066. The cubic root of 21201221 is about 276.7708140023.

Adding to 21201221 its reverse (12210212), we get a palindrome (33411433).

The spelling of 21201221 in words is "twenty-one million, two hundred one thousand, two hundred twenty-one".