21760 has 36 divisors (see below), whose sum is σ = 55188. Its totient is φ = 8192.

The previous prime is 21757. The next prime is 21767. The reversal of 21760 is 6712.

It can be written as a sum of positive squares in 2 ways, for example, as 12544 + 9216 = 112^2 + 96^2 .

It is a Harshad number since it is a multiple of its sum of digits (16).

21760 is an undulating number in base 13.

It is a plaindrome in base 15.

It is a nialpdrome in base 4 and base 16.

It is a zygodrome in base 4, base 15 and base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21767) by changing a digit.

In principle, a polygon with 21760 sides can be constructed with ruler and compass.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1272 + ... + 1288.

It is an arithmetic number, because the mean of its divisors is an integer number (1533).

2²¹⁷⁶⁰ is an apocalyptic number.

21760 is a gapful number since it is divisible by the number (20) 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 21760, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27594).

21760 is an abundant number, since it is smaller than the sum of its proper divisors (33428).

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

21760 is an equidigital number, since it uses as much as digits as its factorization.

21760 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38 (or 24 counting only the distinct ones).

The product of its (nonzero) digits is 84, while the sum is 16.

The square root of 21760 is about 147.5127113167. The cubic root of 21760 is about 27.9181281876.

The spelling of 21760 in words is "twenty-one thousand, seven hundred sixty".