21875 has 12 divisors (see below), whose sum is σ = 31248. Its totient is φ = 15000.

The previous prime is 21871. The next prime is 21881. The reversal of 21875 is 57812.

It is not a de Polignac number, because 21875 - 2² = 21871 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21875.

It is not an unprimeable number, because it can be changed into a prime (21871) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3122 + ... + 3128.

It is an arithmetic number, because the mean of its divisors is an integer number (2604).

21875 is a Friedman number, since it can be written as 5^(7-2)*(8-1), using all its digits and the basic arithmetic operations.

2²¹⁸⁷⁵ is an apocalyptic number.

21875 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21875 is a deficient number, since it is larger than the sum of its proper divisors (9373).

21875 is an frugal number, since it uses more digits than its factorization.

21875 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32 (or 12 counting only the distinct ones).

The product of its digits is 560, while the sum is 23.

The square root of 21875 is about 147.9019945775. The cubic root of 21875 is about 27.9672235520.

Multiplying 21875 by its product of digits (560), we get a square (12250000 = 3500²).

Subtracting 21875 from its reverse (57812), we obtain a cube (35937 = 33³).

The spelling of 21875 in words is "twenty-one thousand, eight hundred seventy-five".