21917 has 8 divisors (see below), whose sum is σ = 26112. Its totient is φ = 18000.

The previous prime is 21911. The next prime is 21929. The reversal of 21917 is 71912.

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

It is a cyclic number.

It is not a de Polignac number, because 21917 - 2⁸ = 21661 is a prime.

It is a Duffinian number.

It is a plaindrome in base 16.

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 21917.

It is not an unprimeable number, because it can be changed into a prime (21911) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 167 + ... + 267.

It is an arithmetic number, because the mean of its divisors is an integer number (3264).

2²¹⁹¹⁷ is an apocalyptic number.

It is an amenable number.

21917 is a deficient number, since it is larger than the sum of its proper divisors (4195).

21917 is a wasteful number, since it uses less digits than its factorization.

21917 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139.

The product of its digits is 126, while the sum is 20.

The square root of 21917 is about 148.0439124044. The cubic root of 21917 is about 27.9851111319.

The spelling of 21917 in words is "twenty-one thousand, nine hundred seventeen".