21456 has 30 divisors (see below), whose sum is σ = 60450. Its totient is φ = 7104.

The previous prime is 21433. The next prime is 21467. The reversal of 21456 is 65412.

It is a happy number.

21456 is nontrivially palindromic in base 15.

It can be written as a sum of positive squares in only one way, i.e., 14400 + 7056 = 120^2 + 84^2 .

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

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an unprimeable number.

21456 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, 70 + ... + 218.

It is an arithmetic number, because the mean of its divisors is an integer number (2015).

2²¹⁴⁵⁶ is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21456, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30225).

21456 is an abundant number, since it is smaller than the sum of its proper divisors (38994).

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

21456 is a wasteful number, since it uses less digits than its factorization.

21456 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 163 (or 154 counting only the distinct ones).

The product of its digits is 240, while the sum is 18.

The square root of 21456 is about 146.4786673888. The cubic root of 21456 is about 27.7875071104.

Adding to 21456 its reverse (65412), we get a palindrome (86868).

Subtracting 21456 from its reverse (65412), we obtain a triangular number (43956 = T₂₉₆).

The spelling of 21456 in words is "twenty-one thousand, four hundred fifty-six".