21716823 has 4 divisors (see below), whose sum is σ = 28955768. Its totient is φ = 14477880.

The previous prime is 21716809. The next prime is 21716831. The reversal of 21716823 is 32861712.

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

It is not a de Polignac number, because 21716823 - 2⁸ = 21716567 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 (21716323) 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, 3619468 + ... + 3619473.

It is an arithmetic number, because the mean of its divisors is an integer number (7238942).

Almost surely, 2^21716823 is an apocalyptic number.

21716823 is a deficient number, since it is larger than the sum of its proper divisors (7238945).

21716823 is an equidigital number, since it uses as much as digits as its factorization.

21716823 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7238944.

The product of its digits is 4032, while the sum is 30.

The square root of 21716823 is about 4660.1312213284. The cubic root of 21716823 is about 278.9965056537.

The spelling of 21716823 in words is "twenty-one million, seven hundred sixteen thousand, eight hundred twenty-three".