21775865 has 4 divisors (see below), whose sum is σ = 26131044. Its totient is φ = 17420688.

The previous prime is 21775837. The next prime is 21775877. The reversal of 21775865 is 56857712.

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 16168441 + 5607424 = 4021^2 + 2368^2 .

It is a cyclic number.

It is not a de Polignac number, because 21775865 - 2¹⁶ = 21710329 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2177582 + ... + 2177591.

It is an arithmetic number, because the mean of its divisors is an integer number (6532761).

Almost surely, 2^21775865 is an apocalyptic number.

It is an amenable number.

21775865 is a deficient number, since it is larger than the sum of its proper divisors (4355179).

21775865 is an equidigital number, since it uses as much as digits as its factorization.

21775865 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4355178.

The product of its digits is 117600, while the sum is 41.

The square root of 21775865 is about 4666.4617216902. The cubic root of 21775865 is about 279.2491148274.

The spelling of 21775865 in words is "twenty-one million, seven hundred seventy-five thousand, eight hundred sixty-five".