21240840 has 32 divisors (see below), whose sum is σ = 63722880. Its totient is φ = 5664192.

The previous prime is 21240833. The next prime is 21240881. The reversal of 21240840 is 4804212.

It is an unprimeable number.

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, 88384 + ... + 88623.

It is an arithmetic number, because the mean of its divisors is an integer number (1991340).

Almost surely, 2^21240840 is an apocalyptic number.

21240840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21240840 is an abundant number, since it is smaller than the sum of its proper divisors (42482040).

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

21240840 is a wasteful number, since it uses less digits than its factorization.

21240840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 177021 (or 177017 counting only the distinct ones).

The product of its (nonzero) digits is 512, while the sum is 21.

The square root of 21240840 is about 4608.7785800578. The cubic root of 21240840 is about 276.9431084750.

The spelling of 21240840 in words is "twenty-one million, two hundred forty thousand, eight hundred forty".