21515 has 8 divisors (see below), whose sum is σ = 27888. Its totient is φ = 15840.

The previous prime is 21503. The next prime is 21517. The reversal of 21515 is 51512.

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

It is not a de Polignac number, because 21515 - 2⁴ = 21499 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21515.

It is not an unprimeable number, because it can be changed into a prime (21517) 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, 101 + ... + 230.

It is an arithmetic number, because the mean of its divisors is an integer number (3486).

2²¹⁵¹⁵ is an apocalyptic number.

21515 is a deficient number, since it is larger than the sum of its proper divisors (6373).

21515 is a wasteful number, since it uses less digits than its factorization.

21515 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 349.

The product of its digits is 50, while the sum is 14.

The square root of 21515 is about 146.6799236433. The cubic root of 21515 is about 27.8129539546.

The spelling of 21515 in words is "twenty-one thousand, five hundred fifteen".