21004321 has 4 divisors (see below), whose sum is σ = 22620052. Its totient is φ = 19388592.

The previous prime is 21004309. The next prime is 21004331. The reversal of 21004321 is 12340012.

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 1299600 + 19704721 = 1140^2 + 4439^2 .

It is a cyclic number.

It is not a de Polignac number, because 21004321 - 2¹⁷ = 20873249 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (13), and also a Moran number because the ratio is a prime number: 1615717 = 21004321 / (2 + 1 + 0 + 0 + 4 + 3 + 2 + 1).

It is not an unprimeable number, because it can be changed into a prime (21004301) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 807846 + ... + 807871.

It is an arithmetic number, because the mean of its divisors is an integer number (5655013).

Almost surely, 2^21004321 is an apocalyptic number.

It is an amenable number.

21004321 is a deficient number, since it is larger than the sum of its proper divisors (1615731).

21004321 is a wasteful number, since it uses less digits than its factorization.

21004321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1615730.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21004321 is about 4583.0471304581. The cubic root of 21004321 is about 275.9113390569.

Adding to 21004321 its reverse (12340012), we get a palindrome (33344333).

The spelling of 21004321 in words is "twenty-one million, four thousand, three hundred twenty-one".