21224240 has 40 divisors (see below), whose sum is σ = 49758720. Its totient is φ = 8418816.

The previous prime is 21224207. The next prime is 21224249. The reversal of 21224240 is 4242212.

It is a happy number.

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 (21224249) 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, 9116 + ... + 11204.

It is an arithmetic number, because the mean of its divisors is an integer number (1243968).

Almost surely, 2^21224240 is an apocalyptic number.

21224240 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 21224240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24879360).

21224240 is an abundant number, since it is smaller than the sum of its proper divisors (28534480).

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

21224240 is a wasteful number, since it uses less digits than its factorization.

21224240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2229 (or 2223 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 17.

The square root of 21224240 is about 4606.9773170703. The cubic root of 21224240 is about 276.8709447607.

Adding to 21224240 its reverse (4242212), we get a palindrome (25466452).

The spelling of 21224240 in words is "twenty-one million, two hundred twenty-four thousand, two hundred forty".