21524240 has 40 divisors (see below), whose sum is σ = 50507928. Its totient is φ = 8529920.

The previous prime is 21524231. The next prime is 21524249. The reversal of 21524240 is 4242512.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21524231) and next prime (21524249).

It can be written as a sum of positive squares in 4 ways, for example, as 2999824 + 18524416 = 1732^2 + 4304^2 .

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

It is a Harshad number since it is a multiple of its sum of digits (20).

It is not an unprimeable number, because it can be changed into a prime (21524249) 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, 7850 + ... + 10230.

Almost surely, 2^21524240 is an apocalyptic number.

21524240 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 21524240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25253964).

21524240 is an abundant number, since it is smaller than the sum of its proper divisors (28983688).

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

21524240 is a wasteful number, since it uses less digits than its factorization.

21524240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2507 (or 2501 counting only the distinct ones).

The product of its (nonzero) digits is 640, while the sum is 20.

The square root of 21524240 is about 4639.4223778397. The cubic root of 21524240 is about 278.1693497428.

Adding to 21524240 its reverse (4242512), we get a palindrome (25766752).

The spelling of 21524240 in words is "twenty-one million, five hundred twenty-four thousand, two hundred forty".