21445565 has 4 divisors (see below), whose sum is σ = 25734684. Its totient is φ = 17156448.

The previous prime is 21445537. The next prime is 21445573. The reversal of 21445565 is 56554412.

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 12313081 + 9132484 = 3509^2 + 3022^2 .

It is a cyclic number.

It is not a de Polignac number, because 21445565 - 2¹⁰ = 21444541 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2144552 + ... + 2144561.

It is an arithmetic number, because the mean of its divisors is an integer number (6433671).

Almost surely, 2^21445565 is an apocalyptic number.

It is an amenable number.

21445565 is a deficient number, since it is larger than the sum of its proper divisors (4289119).

21445565 is an equidigital number, since it uses as much as digits as its factorization.

21445565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4289118.

The product of its digits is 24000, while the sum is 32.

The square root of 21445565 is about 4630.9356506002. The cubic root of 21445565 is about 277.8300161607.

Adding to 21445565 its reverse (56554412), we get a palindrome (77999977).

The spelling of 21445565 in words is "twenty-one million, four hundred forty-five thousand, five hundred sixty-five".