21575 has 6 divisors (see below), whose sum is σ = 26784. Its totient is φ = 17240.

The previous prime is 21569. The next prime is 21577. The reversal of 21575 is 57512.

It is not a de Polignac number, because 21575 - 2⁴ = 21559 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21577) 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 5 ways as a sum of consecutive naturals, for example, 407 + ... + 456.

It is an arithmetic number, because the mean of its divisors is an integer number (4464).

2²¹⁵⁷⁵ is an apocalyptic number.

21575 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21575 is a deficient number, since it is larger than the sum of its proper divisors (5209).

21575 is an equidigital number, since it uses as much as digits as its factorization.

21575 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 873 (or 868 counting only the distinct ones).

The product of its digits is 350, while the sum is 20.

The square root of 21575 is about 146.8843082157. The cubic root of 21575 is about 27.8387844352.

Subtracting 21575 from its reverse (57512), we obtain a cube (35937 = 33³).

The spelling of 21575 in words is "twenty-one thousand, five hundred seventy-five".