21585 has 8 divisors (see below), whose sum is σ = 34560. Its totient is φ = 11504.

The previous prime is 21577. The next prime is 21587. The reversal of 21585 is 58512.

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

It is a cyclic number.

It is not a de Polignac number, because 21585 - 2³ = 21577 is a prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 21585.

It is not an unprimeable number, because it can be changed into a prime (21587) 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, 705 + ... + 734.

It is an arithmetic number, because the mean of its divisors is an integer number (4320).

2²¹⁵⁸⁵ is an apocalyptic number.

It is an amenable number.

21585 is a deficient number, since it is larger than the sum of its proper divisors (12975).

21585 is a wasteful number, since it uses less digits than its factorization.

21585 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1447.

The product of its digits is 400, while the sum is 21.

The square root of 21585 is about 146.9183446681. The cubic root of 21585 is about 27.8430848577.

It can be divided in two parts, 215 and 85, that added together give a triangular number (300 = T₂₄).

The spelling of 21585 in words is "twenty-one thousand, five hundred eighty-five".