21309305 has 8 divisors (see below), whose sum is σ = 25606152. Its totient is φ = 17024128.

The previous prime is 21309289. The next prime is 21309319. The reversal of 21309305 is 50390312.

It is a happy number.

It can be written as a sum of positive squares in 4 ways, for example, as 7862416 + 13446889 = 2804^2 + 3667^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21309305 - 2⁴ = 21309289 is a prime.

It is a Duffinian number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 1799 + ... + 6771.

It is an arithmetic number, because the mean of its divisors is an integer number (3200769).

Almost surely, 2^21309305 is an apocalyptic number.

It is an amenable number.

21309305 is a deficient number, since it is larger than the sum of its proper divisors (4296847).

21309305 is an equidigital number, since it uses as much as digits as its factorization.

21309305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5835.

The product of its (nonzero) digits is 810, while the sum is 23.

The square root of 21309305 is about 4616.2002772843. The cubic root of 21309305 is about 277.2403436482.

Adding to 21309305 its reverse (50390312), we get a palindrome (71699617).

The spelling of 21309305 in words is "twenty-one million, three hundred nine thousand, three hundred five".