21105565 has 12 divisors (see below), whose sum is σ = 27425844. Its totient is φ = 15585024.

The previous prime is 21105563. The next prime is 21105569. The reversal of 21105565 is 56550112.

It can be written as a sum of positive squares in 6 ways, for example, as 10588516 + 10517049 = 3254^2 + 3243^2 .

It is not a de Polignac number, because 21105565 - 2¹ = 21105563 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 (21105563) 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 11 ways as a sum of consecutive naturals, for example, 11644 + ... + 13333.

It is an arithmetic number, because the mean of its divisors is an integer number (2285487).

Almost surely, 2^21105565 is an apocalyptic number.

It is an amenable number.

21105565 is a deficient number, since it is larger than the sum of its proper divisors (6320279).

21105565 is a wasteful number, since it uses less digits than its factorization.

21105565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 25008 (or 24995 counting only the distinct ones).

The product of its (nonzero) digits is 1500, while the sum is 25.

The square root of 21105565 is about 4594.0793419357. The cubic root of 21105565 is about 276.3539401260.

Adding to 21105565 its reverse (56550112), we get a palindrome (77655677).

The spelling of 21105565 in words is "twenty-one million, one hundred five thousand, five hundred sixty-five".