21534240 has 384 divisors, whose sum is σ = 91445760. Its totient is φ = 4128768.

The previous prime is 21534221. The next prime is 21534241. The reversal of 21534240 is 4243512.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21534241) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 742546 + ... + 742574.

It is an arithmetic number, because the mean of its divisors is an integer number (238140).

Almost surely, 2^21534240 is an apocalyptic number.

21534240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is a pronic number, being equal to 4640×4641.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21534240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45722880).

21534240 is an abundant number, since it is smaller than the sum of its proper divisors (69911520).

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

21534240 is a wasteful number, since it uses less digits than its factorization.

21534240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84 (or 76 counting only the distinct ones).

The product of its (nonzero) digits is 960, while the sum is 21.

The square root of 21534240 is about 4640.4999730632. The cubic root of 21534240 is about 278.2124215358.

Adding to 21534240 its reverse (4243512), we get a palindrome (25777752).

The spelling of 21534240 in words is "twenty-one million, five hundred thirty-four thousand, two hundred forty".