21116521 has 4 divisors (see below), whose sum is σ = 21125844. Its totient is φ = 21107200.

The previous prime is 21116519. The next prime is 21116527. The reversal of 21116521 is 12561112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 14356521 + 6760000 = 3789^2 + 2600^2 .

It is a cyclic number.

It is not a de Polignac number, because 21116521 - 2¹ = 21116519 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21116527) 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, 1161 + ... + 6601.

It is an arithmetic number, because the mean of its divisors is an integer number (5281461).

Almost surely, 2^21116521 is an apocalyptic number.

It is an amenable number.

21116521 is a deficient number, since it is larger than the sum of its proper divisors (9323).

21116521 is an equidigital number, since it uses as much as digits as its factorization.

21116521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9322.

The product of its digits is 120, while the sum is 19.

The square root of 21116521 is about 4595.2715915384. The cubic root of 21116521 is about 276.4017507392.

Adding to 21116521 its reverse (12561112), we get a palindrome (33677633).

The spelling of 21116521 in words is "twenty-one million, one hundred sixteen thousand, five hundred twenty-one".