21164521 has 6 divisors (see below), whose sum is σ = 24620010. Its totient is φ = 18140976.

The previous prime is 21164509. The next prime is 21164567. The reversal of 21164521 is 12546112.

It can be written as a sum of positive squares in only one way, i.e., 15093225 + 6071296 = 3885^2 + 2464^2 .

It is not a de Polignac number, because 21164521 - 2⁵ = 21164489 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21164492 and 21164501.

It is not an unprimeable number, because it can be changed into a prime (21164501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 215916 + ... + 216013.

It is an arithmetic number, because the mean of its divisors is an integer number (4103335).

Almost surely, 2^21164521 is an apocalyptic number.

It is an amenable number.

21164521 is a deficient number, since it is larger than the sum of its proper divisors (3455489).

21164521 is an equidigital number, since it uses as much as digits as its factorization.

21164521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 431943 (or 431936 counting only the distinct ones).

The product of its digits is 480, while the sum is 22.

The square root of 21164521 is about 4600.4913867977. The cubic root of 21164521 is about 276.6110220183.

The spelling of 21164521 in words is "twenty-one million, one hundred sixty-four thousand, five hundred twenty-one".