21311305 has 4 divisors (see below), whose sum is σ = 25573572. Its totient is φ = 17049040.

The previous prime is 21311261. The next prime is 21311347. The reversal of 21311305 is 50311312.

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 11923209 + 9388096 = 3453^2 + 3064^2 .

It is not a de Polignac number, because 21311305 - 2⁷ = 21311177 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2131126 + ... + 2131135.

It is an arithmetic number, because the mean of its divisors is an integer number (6393393).

Almost surely, 2^21311305 is an apocalyptic number.

It is an amenable number.

21311305 is a deficient number, since it is larger than the sum of its proper divisors (4262267).

21311305 is an equidigital number, since it uses as much as digits as its factorization.

21311305 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4262266.

The product of its (nonzero) digits is 90, while the sum is 16.

The square root of 21311305 is about 4616.4169005843. The cubic root of 21311305 is about 277.2490169068.

Adding to 21311305 its reverse (50311312), we get a palindrome (71622617).

The spelling of 21311305 in words is "twenty-one million, three hundred eleven thousand, three hundred five".