21243840 has 56 divisors (see below), whose sum is σ = 67452240. Its totient is φ = 5664768.

The previous prime is 21243823. The next prime is 21243841. The reversal of 21243840 is 4834212.

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 21243840.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21243841) 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, 10105 + ... + 12024.

Almost surely, 2^21243840 is an apocalyptic number.

21243840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21243840 is an abundant number, since it is smaller than the sum of its proper divisors (46208400).

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

21243840 is a wasteful number, since it uses less digits than its factorization.

21243840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22149 (or 22139 counting only the distinct ones).

The product of its (nonzero) digits is 1536, while the sum is 24.

The square root of 21243840 is about 4609.1040344084. The cubic root of 21243840 is about 276.9561460983.

The spelling of 21243840 in words is "twenty-one million, two hundred forty-three thousand, eight hundred forty".