21204321 has 16 divisors (see below), whose sum is σ = 31238784. Its totient is φ = 12725504.

The previous prime is 21204251. The next prime is 21204329. The reversal of 21204321 is 12340212.

It is a cyclic number.

It is not a de Polignac number, because 21204321 - 2¹¹ = 21202273 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21204321.

It is not an unprimeable number, because it can be changed into a prime (21204329) 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 15 ways as a sum of consecutive naturals, for example, 7866 + ... + 10211.

It is an arithmetic number, because the mean of its divisors is an integer number (1952424).

Almost surely, 2^21204321 is an apocalyptic number.

It is an amenable number.

21204321 is a deficient number, since it is larger than the sum of its proper divisors (10034463).

21204321 is a wasteful number, since it uses less digits than its factorization.

21204321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18120.

The product of its (nonzero) digits is 96, while the sum is 15.

The square root of 21204321 is about 4604.8149799965. The cubic root of 21204321 is about 276.7843029693.

Adding to 21204321 its reverse (12340212), we get a palindrome (33544533).

It can be divided in two parts, 2120 and 4321, that added together give a triangular number (6441 = T₁₁₃).

The spelling of 21204321 in words is "twenty-one million, two hundred four thousand, three hundred twenty-one".