21286565 has 4 divisors (see below), whose sum is σ = 25543884. Its totient is φ = 17029248.

The previous prime is 21286543. The next prime is 21286579. The reversal of 21286565 is 56568212.

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 4778596 + 16507969 = 2186^2 + 4063^2 .

It is a cyclic number.

It is not a de Polignac number, because 21286565 - 2¹⁴ = 21270181 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, 2128652 + ... + 2128661.

It is an arithmetic number, because the mean of its divisors is an integer number (6385971).

Almost surely, 2^21286565 is an apocalyptic number.

It is an amenable number.

21286565 is a deficient number, since it is larger than the sum of its proper divisors (4257319).

21286565 is an equidigital number, since it uses as much as digits as its factorization.

21286565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4257318.

The product of its digits is 28800, while the sum is 35.

The square root of 21286565 is about 4613.7365551145. The cubic root of 21286565 is about 277.1416905118.

The spelling of 21286565 in words is "twenty-one million, two hundred eighty-six thousand, five hundred sixty-five".