21002321 has 4 divisors (see below), whose sum is σ = 21019812. Its totient is φ = 20984832.

The previous prime is 21002299. The next prime is 21002323. The reversal of 21002321 is 12320012.

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 20830096 + 172225 = 4564^2 + 415^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002321 - 2¹⁸ = 20740177 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21002323) 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, 6800 + ... + 9393.

It is an arithmetic number, because the mean of its divisors is an integer number (5254953).

Almost surely, 2^21002321 is an apocalyptic number.

It is an amenable number.

21002321 is a deficient number, since it is larger than the sum of its proper divisors (17491).

21002321 is a wasteful number, since it uses less digits than its factorization.

21002321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17490.

The product of its (nonzero) digits is 24, while the sum is 11.

The square root of 21002321 is about 4582.8289298205. The cubic root of 21002321 is about 275.9025814907.

Adding to 21002321 its reverse (12320012), we get a palindrome (33322333).

The spelling of 21002321 in words is "twenty-one million, two thousand, three hundred twenty-one".