21715 has 8 divisors (see below), whose sum is σ = 26928. Its totient is φ = 16800.

The previous prime is 21713. The next prime is 21727. The reversal of 21715 is 51712.

21715 is nontrivially palindromic in base 11.

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

It is not a de Polignac number, because 21715 - 2¹ = 21713 is a prime.

It is a Duffinian number.

It is a plaindrome in base 15.

It is a congruent number.

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 7 ways as a sum of consecutive naturals, for example, 165 + ... + 265.

It is an arithmetic number, because the mean of its divisors is an integer number (3366).

2²¹⁷¹⁵ is an apocalyptic number.

21715 is a deficient number, since it is larger than the sum of its proper divisors (5213).

21715 is a wasteful number, since it uses less digits than its factorization.

21715 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149.

The product of its digits is 70, while the sum is 16.

The square root of 21715 is about 147.3601031487. The cubic root of 21715 is about 27.8988698728.

It can be divided in two parts, 217 and 15, that added together give a palindrome (232).

The spelling of 21715 in words is "twenty-one thousand, seven hundred fifteen".