21544440 has 128 divisors (see below), whose sum is σ = 69984000. Its totient is φ = 5285888.

The previous prime is 21544427. The next prime is 21544451. The reversal of 21544440 is 4444512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21544440.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 120271 + ... + 120449.

It is an arithmetic number, because the mean of its divisors is an integer number (546750).

Almost surely, 2^21544440 is an apocalyptic number.

21544440 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 21544440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34992000).

21544440 is an abundant number, since it is smaller than the sum of its proper divisors (48439560).

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

21544440 is a wasteful number, since it uses less digits than its factorization.

21544440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 269 (or 265 counting only the distinct ones).

The product of its (nonzero) digits is 2560, while the sum is 24.

The square root of 21544440 is about 4641.5988624611. The cubic root of 21544440 is about 278.2563410297.

Adding to 21544440 its reverse (4444512), we get a palindrome (25988952).

The spelling of 21544440 in words is "twenty-one million, five hundred forty-four thousand, four hundred forty".