21721713 has 8 divisors (see below), whose sum is σ = 31190208. Its totient is φ = 13367184.

The previous prime is 21721621. The next prime is 21721717. The reversal of 21721713 is 31712712.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21721713 - 2⁸ = 21721457 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21721717) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 278445 + ... + 278522.

It is an arithmetic number, because the mean of its divisors is an integer number (3898776).

Almost surely, 2^21721713 is an apocalyptic number.

It is an amenable number.

21721713 is a deficient number, since it is larger than the sum of its proper divisors (9468495).

21721713 is a wasteful number, since it uses less digits than its factorization.

21721713 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 556983.

The product of its digits is 588, while the sum is 24.

The square root of 21721713 is about 4660.6558551346. The cubic root of 21721713 is about 279.0174447283.

Subtracting 21721713 from its reverse (31712712), we obtain a palindrome (9990999).

The spelling of 21721713 in words is "twenty-one million, seven hundred twenty-one thousand, seven hundred thirteen".