21024 has 36 divisors (see below), whose sum is σ = 60606. Its totient is φ = 6912.

The previous prime is 21023. The next prime is 21031. The reversal of 21024 is 42012.

It is a Cunningham number, because it is equal to 145²-1.

It can be written as a sum of positive squares in only one way, i.e., 17424 + 3600 = 132^2 + 60^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a nialpdrome in base 13 and base 16.

It is a junction number, because it is equal to n+sod(n) for n = 20997 and 21015.

It is not an unprimeable number, because it can be changed into a prime (21023) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 252 + ... + 324.

2²¹⁰²⁴ is an apocalyptic number.

21024 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 21024, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30303).

21024 is an abundant number, since it is smaller than the sum of its proper divisors (39582).

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

21024 is a wasteful number, since it uses less digits than its factorization.

21024 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 89 (or 78 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 9.

The square root of 21024 is about 144.9965516831. The cubic root of 21024 is about 27.5997479498.

Adding to 21024 its reverse (42012), we get a palindrome (63036).

It can be divided in two parts, 2 and 1024, that multiplied together give a 11-th power (2048 = 2¹¹).

The spelling of 21024 in words is "twenty-one thousand, twenty-four", and thus it is an iban number.