21385 has 16 divisors (see below), whose sum is σ = 32256. Its totient is φ = 13248.

The previous prime is 21383. The next prime is 21391. The reversal of 21385 is 58312.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21385 - 2¹ = 21383 is a prime.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21383) 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 15 ways as a sum of consecutive naturals, for example, 432 + ... + 478.

It is an arithmetic number, because the mean of its divisors is an integer number (2016).

2²¹³⁸⁵ is an apocalyptic number.

It is an amenable number.

21385 is a deficient number, since it is larger than the sum of its proper divisors (10871).

21385 is a wasteful number, since it uses less digits than its factorization.

With its successor (21386) it forms an eRAP, since the sums of their prime factors are consecutive (72 and 73).

21385 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72.

The product of its digits is 240, while the sum is 19.

The square root of 21385 is about 146.2361104516. The cubic root of 21385 is about 27.7568227144.

Adding to 21385 its reverse (58312), we get a palindrome (79697).

It can be divided in two parts, 21 and 385, that added together give a triangular number (406 = T₂₈).

The spelling of 21385 in words is "twenty-one thousand, three hundred eighty-five".