21543440 has 40 divisors (see below), whose sum is σ = 51043608. Its totient is φ = 8453120.

The previous prime is 21543439. The next prime is 21543443. The reversal of 21543440 is 4434512.

It can be written as a sum of positive squares in 4 ways, for example, as 1149184 + 20394256 = 1072^2 + 4516^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (21543443) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1700 + ... + 6780.

Almost surely, 2^21543440 is an apocalyptic number.

21543440 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 21543440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25521804).

21543440 is an abundant number, since it is smaller than the sum of its proper divisors (29500168).

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

21543440 is a wasteful number, since it uses less digits than its factorization.

21543440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5147 (or 5141 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 23.

The square root of 21543440 is about 4641.4911397093. The cubic root of 21543440 is about 278.2520358099.

Adding to 21543440 its reverse (4434512), we get a palindrome (25977952).

The spelling of 21543440 in words is "twenty-one million, five hundred forty-three thousand, four hundred forty".