21320809 has 4 divisors (see below), whose sum is σ = 21337216. Its totient is φ = 21304404.

The previous prime is 21320801. The next prime is 21320813. The reversal of 21320809 is 90802312.

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 21320809 - 2³ = 21320801 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21320801) 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 3 ways as a sum of consecutive naturals, for example, 6069 + ... + 8914.

It is an arithmetic number, because the mean of its divisors is an integer number (5334304).

Almost surely, 2^21320809 is an apocalyptic number.

It is an amenable number.

21320809 is a deficient number, since it is larger than the sum of its proper divisors (16407).

21320809 is a wasteful number, since it uses less digits than its factorization.

21320809 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16406.

The product of its (nonzero) digits is 864, while the sum is 25.

The square root of 21320809 is about 4617.4461556146. The cubic root of 21320809 is about 277.2902248175.

The spelling of 21320809 in words is "twenty-one million, three hundred twenty thousand, eight hundred nine".