21312321 has 4 divisors (see below), whose sum is σ = 28416432. Its totient is φ = 14208212.

The previous prime is 21312299. The next prime is 21312323. The reversal of 21312321 is 12321312.

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 21312321 - 2⁵ = 21312289 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21312321.

It is not an unprimeable number, because it can be changed into a prime (21312323) 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, 3552051 + ... + 3552056.

It is an arithmetic number, because the mean of its divisors is an integer number (7104108).

Almost surely, 2^21312321 is an apocalyptic number.

It is an amenable number.

21312321 is a deficient number, since it is larger than the sum of its proper divisors (7104111).

21312321 is an equidigital number, since it uses as much as digits as its factorization.

21312321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7104110.

The product of its digits is 72, while the sum is 15.

The square root of 21312321 is about 4616.5269413272. The cubic root of 21312321 is about 277.2534227144.

Adding to 21312321 its reverse (12321312), we get a palindrome (33633633).

The spelling of 21312321 in words is "twenty-one million, three hundred twelve thousand, three hundred twenty-one".