21565665 has 48 divisors (see below), whose sum is σ = 42943680. Its totient is φ = 9901440.

The previous prime is 21565633. The next prime is 21565667. The reversal of 21565665 is 56656512.

It is a happy number.

It is not a de Polignac number, because 21565665 - 2⁵ = 21565633 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21565667) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 8259 + ... + 10551.

It is an arithmetic number, because the mean of its divisors is an integer number (894660).

Almost surely, 2^21565665 is an apocalyptic number.

It is an amenable number.

21565665 is a deficient number, since it is larger than the sum of its proper divisors (21378015).

21565665 is a wasteful number, since it uses less digits than its factorization.

21565665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2334 (or 2331 counting only the distinct ones).

The product of its digits is 54000, while the sum is 36.

The square root of 21565665 is about 4643.8846884909. The cubic root of 21565665 is about 278.3476879143.

The spelling of 21565665 in words is "twenty-one million, five hundred sixty-five thousand, six hundred sixty-five".