21306305 has 4 divisors (see below), whose sum is σ = 25567572. Its totient is φ = 17045040.

The previous prime is 21306301. The next prime is 21306317. The reversal of 21306305 is 50360312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 13017664 + 8288641 = 3608^2 + 2879^2 .

It is not a de Polignac number, because 21306305 - 2² = 21306301 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21306301) 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, 2130626 + ... + 2130635.

It is an arithmetic number, because the mean of its divisors is an integer number (6391893).

Almost surely, 2^21306305 is an apocalyptic number.

It is an amenable number.

21306305 is a deficient number, since it is larger than the sum of its proper divisors (4261267).

21306305 is an equidigital number, since it uses as much as digits as its factorization.

21306305 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4261266.

The product of its (nonzero) digits is 540, while the sum is 20.

The square root of 21306305 is about 4615.8753232729. The cubic root of 21306305 is about 277.2273327426.

Adding to 21306305 its reverse (50360312), we get a palindrome (71666617).

The spelling of 21306305 in words is "twenty-one million, three hundred six thousand, three hundred five".