21864565 has 4 divisors (see below), whose sum is σ = 26237484. Its totient is φ = 17491648.

The previous prime is 21864553. The next prime is 21864569. The reversal of 21864565 is 56546812.

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 9523396 + 12341169 = 3086^2 + 3513^2 .

It is a cyclic number.

It is not a de Polignac number, because 21864565 - 2¹¹ = 21862517 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 (21864569) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2186452 + ... + 2186461.

It is an arithmetic number, because the mean of its divisors is an integer number (6559371).

Almost surely, 2^21864565 is an apocalyptic number.

It is an amenable number.

21864565 is a deficient number, since it is larger than the sum of its proper divisors (4372919).

21864565 is an equidigital number, since it uses as much as digits as its factorization.

21864565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4372918.

The product of its digits is 57600, while the sum is 37.

The square root of 21864565 is about 4675.9560519748. The cubic root of 21864565 is about 279.6277578982.

The spelling of 21864565 in words is "twenty-one million, eight hundred sixty-four thousand, five hundred sixty-five".