21320321 has 6 divisors (see below), whose sum is σ = 23434866. Its totient is φ = 19382000.

The previous prime is 21320317. The next prime is 21320323. The reversal of 21320321 is 12302312.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 15249025 + 6071296 = 3905^2 + 2464^2 .

It is not a de Polignac number, because 21320321 - 2² = 21320317 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21320296 and 21320305.

It is not an unprimeable number, because it can be changed into a prime (21320323) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 87980 + ... + 88221.

It is an arithmetic number, because the mean of its divisors is an integer number (3905811).

Almost surely, 2^21320321 is an apocalyptic number.

It is an amenable number.

21320321 is a deficient number, since it is larger than the sum of its proper divisors (2114545).

21320321 is a wasteful number, since it uses less digits than its factorization.

21320321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 176223 (or 176212 counting only the distinct ones).

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

The square root of 21320321 is about 4617.3933122488. The cubic root of 21320321 is about 277.2881092213.

Adding to 21320321 its reverse (12302312), we get a palindrome (33622633).

Subtracting from 21320321 its reverse (12302312), we obtain a square (9018009 = 3003²).

The spelling of 21320321 in words is "twenty-one million, three hundred twenty thousand, three hundred twenty-one".