21147205 has 4 divisors (see below), whose sum is σ = 25376652. Its totient is φ = 16917760.

The previous prime is 21147197. The next prime is 21147211. The reversal of 21147205 is 50274112.

It is a happy number.

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 12397441 + 8749764 = 3521^2 + 2958^2 .

It is not a de Polignac number, because 21147205 - 2³ = 21147197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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, 2114716 + ... + 2114725.

It is an arithmetic number, because the mean of its divisors is an integer number (6344163).

Almost surely, 2^21147205 is an apocalyptic number.

It is an amenable number.

21147205 is a deficient number, since it is larger than the sum of its proper divisors (4229447).

21147205 is an equidigital number, since it uses as much as digits as its factorization.

21147205 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4229446.

The product of its (nonzero) digits is 560, while the sum is 22.

The square root of 21147205 is about 4598.6090288260. The cubic root of 21147205 is about 276.5355639231.

The spelling of 21147205 in words is "twenty-one million, one hundred forty-seven thousand, two hundred five".