21087565 has 8 divisors (see below), whose sum is σ = 26793720. Its totient is φ = 15877632.

The previous prime is 21087557. The next prime is 21087569. The reversal of 21087565 is 56578012.

It can be written as a sum of positive squares in 4 ways, for example, as 6563844 + 14523721 = 2562^2 + 3811^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21087565 - 2³ = 21087557 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21087565.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21087569) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 123960 + ... + 124129.

It is an arithmetic number, because the mean of its divisors is an integer number (3349215).

Almost surely, 2^21087565 is an apocalyptic number.

It is an amenable number.

21087565 is a deficient number, since it is larger than the sum of its proper divisors (5706155).

21087565 is a wasteful number, since it uses less digits than its factorization.

21087565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 248111.

The product of its (nonzero) digits is 16800, while the sum is 34.

The square root of 21087565 is about 4592.1198808393. The cubic root of 21087565 is about 276.2753544428.

The spelling of 21087565 in words is "twenty-one million, eighty-seven thousand, five hundred sixty-five".