21042440 has 32 divisors (see below), whose sum is σ = 47952000. Its totient is φ = 8309184.

The previous prime is 21042419. The next prime is 21042449. The reversal of 21042440 is 4424012.

It is not an unprimeable number, because it can be changed into a prime (21042449) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 170 + ... + 6489.

It is an arithmetic number, because the mean of its divisors is an integer number (1498500).

Almost surely, 2^21042440 is an apocalyptic number.

21042440 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 21042440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23976000).

21042440 is an abundant number, since it is smaller than the sum of its proper divisors (26909560).

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

21042440 is a wasteful number, since it uses less digits than its factorization.

21042440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6749 (or 6745 counting only the distinct ones).

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

The square root of 21042440 is about 4587.2039414005. The cubic root of 21042440 is about 276.0781477231.

Adding to 21042440 its reverse (4424012), we get a palindrome (25466452).

The spelling of 21042440 in words is "twenty-one million, forty-two thousand, four hundred forty".