21750 has 32 divisors (see below), whose sum is σ = 56160. Its totient is φ = 5600.

The previous prime is 21739. The next prime is 21751. The reversal of 21750 is 5712.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is an Ulam number.

It is a zygodrome in base 5.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21751) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 736 + ... + 764.

It is an arithmetic number, because the mean of its divisors is an integer number (1755).

2²¹⁷⁵⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21750, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28080).

21750 is an abundant number, since it is smaller than the sum of its proper divisors (34410).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21750 is a wasteful number, since it uses less digits than its factorization.

21750 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49 (or 39 counting only the distinct ones).

The product of its (nonzero) digits is 70, while the sum is 15.

The square root of 21750 is about 147.4788120375. The cubic root of 21750 is about 27.9138508583.

The spelling of 21750 in words is "twenty-one thousand, seven hundred fifty".