21804221 has 4 divisors (see below), whose sum is σ = 21815772. Its totient is φ = 21792672.

The previous prime is 21804197. The next prime is 21804227. The reversal of 21804221 is 12240812.

It is a happy number.

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 3648100 + 18156121 = 1910^2 + 4261^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21804221 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21804193 and 21804202.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21804227) 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, 2210 + ... + 6963.

It is an arithmetic number, because the mean of its divisors is an integer number (5453943).

Almost surely, 2^21804221 is an apocalyptic number.

It is an amenable number.

21804221 is a deficient number, since it is larger than the sum of its proper divisors (11551).

21804221 is an equidigital number, since it uses as much as digits as its factorization.

21804221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11550.

The product of its (nonzero) digits is 256, while the sum is 20.

The square root of 21804221 is about 4669.4990095298. The cubic root of 21804221 is about 279.3702727139.

The spelling of 21804221 in words is "twenty-one million, eight hundred four thousand, two hundred twenty-one".