21316521 has 16 divisors (see below), whose sum is σ = 30737664. Its totient is φ = 13089024.

The previous prime is 21316513. The next prime is 21316531. The reversal of 21316521 is 12561312.

It is not a de Polignac number, because 21316521 - 2³ = 21316513 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21316501) 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 15 ways as a sum of consecutive naturals, for example, 2050 + ... + 6843.

It is an arithmetic number, because the mean of its divisors is an integer number (1921104).

Almost surely, 2^21316521 is an apocalyptic number.

It is an amenable number.

21316521 is a deficient number, since it is larger than the sum of its proper divisors (9421143).

21316521 is a wasteful number, since it uses less digits than its factorization.

21316521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8960.

The product of its digits is 360, while the sum is 21.

The square root of 21316521 is about 4616.9818063319. The cubic root of 21316521 is about 277.2716342126.

Adding to 21316521 its reverse (12561312), we get a palindrome (33877833).

The spelling of 21316521 in words is "twenty-one million, three hundred sixteen thousand, five hundred twenty-one".