21128665 has 16 divisors (see below), whose sum is σ = 27414720. Its totient is φ = 15577920.

The previous prime is 21128659. The next prime is 21128683. The reversal of 21128665 is 56682112.

It is not a de Polignac number, because 21128665 - 2⁵ = 21128633 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 510 + ... + 6520.

It is an arithmetic number, because the mean of its divisors is an integer number (1713420).

Almost surely, 2^21128665 is an apocalyptic number.

It is an amenable number.

21128665 is a deficient number, since it is larger than the sum of its proper divisors (6286055).

21128665 is a wasteful number, since it uses less digits than its factorization.

21128665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6072.

The product of its digits is 5760, while the sum is 31.

The square root of 21128665 is about 4596.5927598603. The cubic root of 21128665 is about 276.4547263155.

The spelling of 21128665 in words is "twenty-one million, one hundred twenty-eight thousand, six hundred sixty-five".