21320521 has 4 divisors (see below), whose sum is σ = 21414672. Its totient is φ = 21226372.

The previous prime is 21320513. The next prime is 21320531. The reversal of 21320521 is 12502312.

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 21320521 - 2³ = 21320513 is a prime.

It is a super-2 number, since 2×21320521² = 909129231422882, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21320495 and 21320504.

It is not an unprimeable number, because it can be changed into a prime (21320531) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 46735 + ... + 47188.

It is an arithmetic number, because the mean of its divisors is an integer number (5353668).

Almost surely, 2^21320521 is an apocalyptic number.

It is an amenable number.

21320521 is a deficient number, since it is larger than the sum of its proper divisors (94151).

21320521 is an equidigital number, since it uses as much as digits as its factorization.

21320521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94150.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 21320521 is about 4617.4149694391. The cubic root of 21320521 is about 277.2889762728.

Adding to 21320521 its reverse (12502312), we get a palindrome (33822833).

The spelling of 21320521 in words is "twenty-one million, three hundred twenty thousand, five hundred twenty-one".