21128047 has 4 divisors (see below), whose sum is σ = 21197176. Its totient is φ = 21058920.

The previous prime is 21128033. The next prime is 21128069. The reversal of 21128047 is 74082112.

It is a happy number.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21128047 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21128017) by changing a digit.

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 3 ways as a sum of consecutive naturals, for example, 34104 + ... + 34717.

It is an arithmetic number, because the mean of its divisors is an integer number (5299294).

Almost surely, 2^21128047 is an apocalyptic number.

21128047 is a deficient number, since it is larger than the sum of its proper divisors (69129).

21128047 is an equidigital number, since it uses as much as digits as its factorization.

21128047 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 69128.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 21128047 is about 4596.5255356628. The cubic root of 21128047 is about 276.4520309143.

The spelling of 21128047 in words is "twenty-one million, one hundred twenty-eight thousand, forty-seven".