21147709 has 4 divisors (see below), whose sum is σ = 23070240. Its totient is φ = 19225180.

The previous prime is 21147671. The next prime is 21147713. The reversal of 21147709 is 90774112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21147709 - 2⁹ = 21147197 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21147739) 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, 961249 + ... + 961270.

It is an arithmetic number, because the mean of its divisors is an integer number (5767560).

Almost surely, 2^21147709 is an apocalyptic number.

It is an amenable number.

21147709 is a deficient number, since it is larger than the sum of its proper divisors (1922531).

21147709 is a wasteful number, since it uses less digits than its factorization.

21147709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1922530.

The product of its (nonzero) digits is 3528, while the sum is 31.

The square root of 21147709 is about 4598.6638276786. The cubic root of 21147709 is about 276.5377607905.

The spelling of 21147709 in words is "twenty-one million, one hundred forty-seven thousand, seven hundred nine".