21915 has 12 divisors (see below), whose sum is σ = 38064. Its totient is φ = 11664.

The previous prime is 21911. The next prime is 21929. The reversal of 21915 is 51912.

It is not a de Polignac number, because 21915 - 2² = 21911 is a prime.

21915 is a lucky number.

It is a plaindrome in base 16.

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 11 ways as a sum of consecutive naturals, for example, 199 + ... + 288.

It is an arithmetic number, because the mean of its divisors is an integer number (3172).

2²¹⁹¹⁵ is an apocalyptic number.

21915 is a deficient number, since it is larger than the sum of its proper divisors (16149).

21915 is a wasteful number, since it uses less digits than its factorization.

21915 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 498 (or 495 counting only the distinct ones).

The product of its digits is 90, while the sum is 18.

The square root of 21915 is about 148.0371574977. The cubic root of 21915 is about 27.9842598609.

The spelling of 21915 in words is "twenty-one thousand, nine hundred fifteen".