21921565 has 4 divisors (see below), whose sum is σ = 26305884. Its totient is φ = 17537248.

The previous prime is 21921563. The next prime is 21921577. The reversal of 21921565 is 56512912.

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 7986276 + 13935289 = 2826^2 + 3733^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921565 - 2¹ = 21921563 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21921563) 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, 2192152 + ... + 2192161.

It is an arithmetic number, because the mean of its divisors is an integer number (6576471).

Almost surely, 2^21921565 is an apocalyptic number.

It is an amenable number.

21921565 is a deficient number, since it is larger than the sum of its proper divisors (4384319).

21921565 is an equidigital number, since it uses as much as digits as its factorization.

21921565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4384318.

The product of its digits is 5400, while the sum is 31.

The square root of 21921565 is about 4682.0470950216. The cubic root of 21921565 is about 279.8705396419.

The spelling of 21921565 in words is "twenty-one million, nine hundred twenty-one thousand, five hundred sixty-five".