21165009 has 4 divisors (see below), whose sum is σ = 28220016. Its totient is φ = 14110004.

The previous prime is 21165007. The next prime is 21165019. The reversal of 21165009 is 90056112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21165009 - 2¹ = 21165007 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21165009.

It is not an unprimeable number, because it can be changed into a prime (21165007) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3527499 + ... + 3527504.

It is an arithmetic number, because the mean of its divisors is an integer number (7055004).

Almost surely, 2^21165009 is an apocalyptic number.

It is an amenable number.

21165009 is a deficient number, since it is larger than the sum of its proper divisors (7055007).

21165009 is an equidigital number, since it uses as much as digits as its factorization.

21165009 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7055006.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 21165009 is about 4600.5444243046. The cubic root of 21165009 is about 276.6131479841.

The spelling of 21165009 in words is "twenty-one million, one hundred sixty-five thousand, nine".