21606909 has 4 divisors (see below), whose sum is σ = 28809216. Its totient is φ = 14404604.

The previous prime is 21606899. The next prime is 21606917. The reversal of 21606909 is 90960612.

It is a happy number.

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 21606909 - 2¹⁵ = 21574141 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21606909.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21606979) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3601149 + ... + 3601154.

It is an arithmetic number, because the mean of its divisors is an integer number (7202304).

Almost surely, 2^21606909 is an apocalyptic number.

It is an amenable number.

21606909 is a deficient number, since it is larger than the sum of its proper divisors (7202307).

21606909 is an equidigital number, since it uses as much as digits as its factorization.

21606909 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7202306.

The product of its (nonzero) digits is 5832, while the sum is 33.

The square root of 21606909 is about 4648.3232460749. The cubic root of 21606909 is about 278.5250201267.

The spelling of 21606909 in words is "twenty-one million, six hundred six thousand, nine hundred nine".