21717 has 12 divisors (see below), whose sum is σ = 33280. Its totient is φ = 13608.

The previous prime is 21713. The next prime is 21727. The reversal of 21717 is 71712.

21717 = T₃₈ + T₃₉ + ... + T₅₆.

21717 is nontrivially palindromic in base 8.

It is not a de Polignac number, because 21717 - 2² = 21713 is a prime.

It is a Duffinian number.

21717 is a lucky number.

It is a plaindrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 21717.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21717.

It is not an unprimeable number, because it can be changed into a prime (21713) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 108 + ... + 234.

2²¹⁷¹⁷ is an apocalyptic number.

It is an amenable number.

21717 is a deficient number, since it is larger than the sum of its proper divisors (11563).

21717 is a wasteful number, since it uses less digits than its factorization.

21717 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 152 (or 149 counting only the distinct ones).

The product of its digits is 98, while the sum is 18.

The square root of 21717 is about 147.3668890898. The cubic root of 21717 is about 27.8997263626.

The spelling of 21717 in words is "twenty-one thousand, seven hundred seventeen", and thus it is an iban number.