21724613 has 2 divisors, whose sum is σ = 21724614. Its totient is φ = 21724612.

The previous prime is 21724609. The next prime is 21724621. The reversal of 21724613 is 31642712.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20638849 + 1085764 = 4543^2 + 1042^2 .

It is a cyclic number.

It is not a de Polignac number, because 21724613 - 2² = 21724609 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21724663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10862306 + 10862307.

It is an arithmetic number, because the mean of its divisors is an integer number (10862307).

Almost surely, 2^21724613 is an apocalyptic number.

It is an amenable number.

21724613 is a deficient number, since it is larger than the sum of its proper divisors (1).

21724613 is an equidigital number, since it uses as much as digits as its factorization.

21724613 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 26.

The square root of 21724613 is about 4660.9669597627. The cubic root of 21724613 is about 279.0298610999.

The spelling of 21724613 in words is "twenty-one million, seven hundred twenty-four thousand, six hundred thirteen".