21566723 has 4 divisors (see below), whose sum is σ = 21587280. Its totient is φ = 21546168.

The previous prime is 21566719. The next prime is 21566737. The reversal of 21566723 is 32766512.

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

It is a cyclic number.

It is not a de Polignac number, because 21566723 - 2² = 21566719 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21566723.

It is not an unprimeable number, because it can be changed into a prime (21566323) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8615 + ... + 10832.

It is an arithmetic number, because the mean of its divisors is an integer number (5396820).

Almost surely, 2^21566723 is an apocalyptic number.

21566723 is a deficient number, since it is larger than the sum of its proper divisors (20557).

21566723 is a wasteful number, since it uses less digits than its factorization.

21566723 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20556.

The product of its digits is 15120, while the sum is 32.

The square root of 21566723 is about 4643.9986003443. The cubic root of 21566723 is about 278.3522397028.

The spelling of 21566723 in words is "twenty-one million, five hundred sixty-six thousand, seven hundred twenty-three".