21308609 has 4 divisors (see below), whose sum is σ = 24352704. Its totient is φ = 18264516.

The previous prime is 21308579. The next prime is 21308611. The reversal of 21308609 is 90680312.

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 a de Polignac number, because none of the positive numbers 2^k-21308609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21308629) 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, 1522037 + ... + 1522050.

It is an arithmetic number, because the mean of its divisors is an integer number (6088176).

Almost surely, 2^21308609 is an apocalyptic number.

It is an amenable number.

21308609 is a deficient number, since it is larger than the sum of its proper divisors (3044095).

21308609 is an equidigital number, since it uses as much as digits as its factorization.

21308609 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3044094.

The product of its (nonzero) digits is 2592, while the sum is 29.

The square root of 21308609 is about 4616.1248899916. The cubic root of 21308609 is about 277.2373252269.

The spelling of 21308609 in words is "twenty-one million, three hundred eight thousand, six hundred nine".