21088565 has 4 divisors (see below), whose sum is σ = 25306284. Its totient is φ = 16870848.

The previous prime is 21088559. The next prime is 21088567. The reversal of 21088565 is 56588012.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 15547249 + 5541316 = 3943^2 + 2354^2 .

It is a cyclic number.

It is not a de Polignac number, because 21088565 - 2⁴ = 21088549 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21088567) 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, 2108852 + ... + 2108861.

It is an arithmetic number, because the mean of its divisors is an integer number (6326571).

Almost surely, 2^21088565 is an apocalyptic number.

It is an amenable number.

21088565 is a deficient number, since it is larger than the sum of its proper divisors (4217719).

21088565 is an equidigital number, since it uses as much as digits as its factorization.

21088565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4217718.

The product of its (nonzero) digits is 19200, while the sum is 35.

The square root of 21088565 is about 4592.2287617234. The cubic root of 21088565 is about 276.2797214870.

The spelling of 21088565 in words is "twenty-one million, eighty-eight thousand, five hundred sixty-five".