21960 has 48 divisors (see below), whose sum is σ = 72540. Its totient is φ = 5760.

The previous prime is 21943. The next prime is 21961. The reversal of 21960 is 6912.

21960 is nontrivially palindromic in base 14.

It can be written as a sum of positive squares in 2 ways, for example, as 19044 + 2916 = 138^2 + 54^2 .

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

It is a nialpdrome in base 9.

It is not an unprimeable number, because it can be changed into a prime (21961) by changing a digit.

21960 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 11 ways as a sum of consecutive naturals, for example, 330 + ... + 390.

2²¹⁹⁶⁰ is an apocalyptic number.

21960 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 21960, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36270).

21960 is an abundant number, since it is smaller than the sum of its proper divisors (50580).

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

21960 is a wasteful number, since it uses less digits than its factorization.

21960 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 78 (or 71 counting only the distinct ones).

The product of its (nonzero) digits is 108, while the sum is 18.

The square root of 21960 is about 148.1890684227. The cubic root of 21960 is about 28.0034009474.

The spelling of 21960 in words is "twenty-one thousand, nine hundred sixty".