21203840 has 64 divisors (see below), whose sum is σ = 57944160. Its totient is φ = 7268352.

The previous prime is 21203827. The next prime is 21203851. The reversal of 21203840 is 4830212.

It is a tau number, because it is divible by the number of its divisors (64).

It is a Harshad number since it is a multiple of its sum of digits (20).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2114 + ... + 6846.

Almost surely, 2^21203840 is an apocalyptic number.

21203840 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 21203840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28972080).

21203840 is an abundant number, since it is smaller than the sum of its proper divisors (36740320).

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

21203840 is an equidigital number, since it uses as much as digits as its factorization.

21203840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4759 (or 4747 counting only the distinct ones).

The product of its (nonzero) digits is 384, while the sum is 20.

The square root of 21203840 is about 4604.7627517604. The cubic root of 21203840 is about 276.7822100899.

The spelling of 21203840 in words is "twenty-one million, two hundred three thousand, eight hundred forty".