21723613 has 4 divisors (see below), whose sum is σ = 21733180. Its totient is φ = 21714048.

The previous prime is 21723589. The next prime is 21723641. The reversal of 21723613 is 31632712.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 14122564 + 7601049 = 3758^2 + 2757^2 .

It is a cyclic number.

It is not a de Polignac number, because 21723613 - 2⁹ = 21723101 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 (21723113) 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, 781 + ... + 6637.

It is an arithmetic number, because the mean of its divisors is an integer number (5433295).

Almost surely, 2^21723613 is an apocalyptic number.

It is an amenable number.

21723613 is a deficient number, since it is larger than the sum of its proper divisors (9567).

21723613 is an equidigital number, since it uses as much as digits as its factorization.

21723613 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9566.

The product of its digits is 1512, while the sum is 25.

The square root of 21723613 is about 4660.8596846505. The cubic root of 21723613 is about 279.0255797173.

Subtracting 21723613 from its reverse (31632712), we obtain a palindrome (9909099).

The spelling of 21723613 in words is "twenty-one million, seven hundred twenty-three thousand, six hundred thirteen".