21744 has 30 divisors (see below), whose sum is σ = 61256. Its totient is φ = 7200.

The previous prime is 21739. The next prime is 21751. The reversal of 21744 is 44712.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a plaindrome in base 15.

It is a zygodrome in base 15.

It is a congruent number.

It is an unprimeable number.

21744 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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, 69 + ... + 219.

2²¹⁷⁴⁴ is an apocalyptic number.

21744 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21744, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30628).

21744 is an abundant number, since it is smaller than the sum of its proper divisors (39512).

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

21744 is a wasteful number, since it uses less digits than its factorization.

21744 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 165 (or 156 counting only the distinct ones).

The product of its digits is 224, while the sum is 18.

The square root of 21744 is about 147.4584687293. The cubic root of 21744 is about 27.9112838313.

The spelling of 21744 in words is "twenty-one thousand, seven hundred forty-four", and thus it is an iban number.