21445440 has 112 divisors (see below), whose sum is σ = 69128640. Its totient is φ = 5632000.

The previous prime is 21445409. The next prime is 21445441. The reversal of 21445440 is 4454412.

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 21445440.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21445441) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 85315 + ... + 85565.

It is an arithmetic number, because the mean of its divisors is an integer number (617220).

Almost surely, 2^21445440 is an apocalyptic number.

21445440 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 21445440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34564320).

21445440 is an abundant number, since it is smaller than the sum of its proper divisors (47683200).

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

21445440 is a wasteful number, since it uses less digits than its factorization.

21445440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 360 (or 350 counting only the distinct ones).

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

The square root of 21445440 is about 4630.9221543878. The cubic root of 21445440 is about 277.8294763627.

Adding to 21445440 its reverse (4454412), we get a palindrome (25899852).

It can be divided in two parts, 214 and 45440, that added together give a palindrome (45654).

The spelling of 21445440 in words is "twenty-one million, four hundred forty-five thousand, four hundred forty".