21725665 has 16 divisors (see below), whose sum is σ = 28421568. Its totient is φ = 15846336.

The previous prime is 21725663. The next prime is 21725689. The reversal of 21725665 is 56652712.

It is a cyclic number.

It is not a de Polignac number, because 21725665 - 2¹ = 21725663 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21725665.

It is not an unprimeable number, because it can be changed into a prime (21725663) 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 15 ways as a sum of consecutive naturals, for example, 3382 + ... + 7408.

It is an arithmetic number, because the mean of its divisors is an integer number (1776348).

Almost surely, 2^21725665 is an apocalyptic number.

It is an amenable number.

21725665 is a deficient number, since it is larger than the sum of its proper divisors (6695903).

21725665 is a wasteful number, since it uses less digits than its factorization.

21725665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4128.

The product of its digits is 25200, while the sum is 34.

The square root of 21725665 is about 4661.0798105160. The cubic root of 21725665 is about 279.0343649726.

The spelling of 21725665 in words is "twenty-one million, seven hundred twenty-five thousand, six hundred sixty-five".