21375 has 24 divisors (see below), whose sum is σ = 40560. Its totient is φ = 10800.

The previous prime is 21347. The next prime is 21377. The reversal of 21375 is 57312.

It is not a de Polignac number, because 21375 - 2⁷ = 21247 is a prime.

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

It is a nialpdrome in base 13 and base 15.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21377) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1116 + ... + 1134.

It is an arithmetic number, because the mean of its divisors is an integer number (1690).

21375 is a Friedman number, since it can be written as 7125*3, using all its digits and the basic arithmetic operations.

2²¹³⁷⁵ is an apocalyptic number.

21375 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21375 is a deficient number, since it is larger than the sum of its proper divisors (19185).

21375 is a wasteful number, since it uses less digits than its factorization.

21375 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 40 (or 27 counting only the distinct ones).

The product of its digits is 210, while the sum is 18.

The square root of 21375 is about 146.2019151721. The cubic root of 21375 is about 27.7524955146.

Adding to 21375 its reverse (57312), we get a palindrome (78687).

Subtracting 21375 from its reverse (57312), we obtain a cube (35937 = 33³).

It can be divided in two parts, 21 and 375, that multiplied together give a triangular number (7875 = T₁₂₅).

The spelling of 21375 in words is "twenty-one thousand, three hundred seventy-five".