21784840 has 96 divisors (see below), whose sum is σ = 61669440. Its totient is φ = 6779520.

The previous prime is 21784831. The next prime is 21784853. The reversal of 21784840 is 4848712.

It is a junction number, because it is equal to n+sod(n) for n = 21784796 and 21784805.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 33559 + ... + 34201.

It is an arithmetic number, because the mean of its divisors is an integer number (642390).

Almost surely, 2^21784840 is an apocalyptic number.

21784840 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 21784840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30834720).

21784840 is an abundant number, since it is smaller than the sum of its proper divisors (39884600).

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

21784840 is a wasteful number, since it uses less digits than its factorization.

21784840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 683 (or 668 counting only the distinct ones).

The product of its (nonzero) digits is 14336, while the sum is 34.

The square root of 21784840 is about 4667.4232719992. The cubic root of 21784840 is about 279.2874740623.

The spelling of 21784840 in words is "twenty-one million, seven hundred eighty-four thousand, eight hundred forty".