21648 has 40 divisors (see below), whose sum is σ = 62496. Its totient is φ = 6400.

The previous prime is 21647. The next prime is 21649. The reversal of 21648 is 84612.

21648 is nontrivially palindromic in base 9.

It is an interprime number because it is at equal distance from previous prime (21647) and next prime (21649).

It is a nude number because it is divisible by every one of its digits.

It is one of the 548 Lynch-Bell numbers.

It is a nialpdrome in base 8 and base 15.

It is a zygodrome in base 15.

It is not an unprimeable number, because it can be changed into a prime (21647) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 508 + ... + 548.

2²¹⁶⁴⁸ 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 21648, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31248).

21648 is an abundant number, since it is smaller than the sum of its proper divisors (40848).

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

21648 is a wasteful number, since it uses less digits than its factorization.

21648 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 63 (or 57 counting only the distinct ones).

The product of its digits is 384, while the sum is 21.

The square root of 21648 is about 147.1325932620. The cubic root of 21648 is about 27.8701470233.

The spelling of 21648 in words is "twenty-one thousand, six hundred forty-eight".