21204221 has 4 divisors (see below), whose sum is σ = 21502944. Its totient is φ = 20905500.

The previous prime is 21204199. The next prime is 21204223. The reversal of 21204221 is 12240212.

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 a cyclic number.

It is not a de Polignac number, because 21204221 - 2¹⁰ = 21203197 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21204196 and 21204205.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21204223) 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, 149255 + ... + 149396.

It is an arithmetic number, because the mean of its divisors is an integer number (5375736).

Almost surely, 2^21204221 is an apocalyptic number.

It is an amenable number.

21204221 is a deficient number, since it is larger than the sum of its proper divisors (298723).

21204221 is an equidigital number, since it uses as much as digits as its factorization.

21204221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 298722.

The product of its (nonzero) digits is 64, while the sum is 14.

The square root of 21204221 is about 4604.8041217841. The cubic root of 21204221 is about 276.7838678618.

Adding to 21204221 its reverse (12240212), we get a palindrome (33444433).

The spelling of 21204221 in words is "twenty-one million, two hundred four thousand, two hundred twenty-one".