21312320 has 28 divisors (see below), whose sum is σ = 50750724. Its totient is φ = 8524800.

The previous prime is 21312299. The next prime is 21312323. The reversal of 21312320 is 2321312.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 12503296 + 8809024 = 3536^2 + 2968^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21312295 and 21312304.

It is a congruent number.

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, 32981 + ... + 33620.

Almost surely, 2^21312320 is an apocalyptic number.

21312320 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21312320 is an abundant number, since it is smaller than the sum of its proper divisors (29438404).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21312320 is an equidigital number, since it uses as much as digits as its factorization.

21312320 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 66618 (or 66608 counting only the distinct ones).

The product of its (nonzero) digits is 72, while the sum is 14.

The square root of 21312320 is about 4616.5268330207. The cubic root of 21312320 is about 277.2534183780.

Adding to 21312320 its reverse (2321312), we get a palindrome (23633632).

The spelling of 21312320 in words is "twenty-one million, three hundred twelve thousand, three hundred twenty".