21315 has 24 divisors (see below), whose sum is σ = 41040. Its totient is φ = 9408.

The previous prime is 21313. The next prime is 21317. The reversal of 21315 is 51312.

21315 is nontrivially palindromic in base 14.

It is a Cunningham number, because it is equal to 146²-1.

It is an interprime number because it is at equal distance from previous prime (21313) and next prime (21317).

It is not a de Polignac number, because 21315 - 2¹ = 21313 is a prime.

21315 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 21315.

It is not an unprimeable number, because it can be changed into a prime (21313) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 721 + ... + 749.

It is an arithmetic number, because the mean of its divisors is an integer number (1710).

2²¹³¹⁵ is an apocalyptic number.

21315 is a deficient number, since it is larger than the sum of its proper divisors (19725).

21315 is a wasteful number, since it uses less digits than its factorization.

21315 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51 (or 44 counting only the distinct ones).

The product of its digits is 30, while the sum is 12.

The square root of 21315 is about 145.9965753023. The cubic root of 21315 is about 27.7265039325.

Adding to 21315 its reverse (51312), we get a palindrome (72627).

The spelling of 21315 in words is "twenty-one thousand, three hundred fifteen".