21720832 has 144 divisors (see below), whose sum is σ = 56512512. Its totient is φ = 8110080.

The previous prime is 21720827. The next prime is 21720833. The reversal of 21720832 is 23802712.

It is a junction number, because it is equal to n+sod(n) for n = 21720797 and 21720806.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21720833) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 700657 + ... + 700687.

It is an arithmetic number, because the mean of its divisors is an integer number (392448).

Almost surely, 2^21720832 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21720832, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28256256).

21720832 is an abundant number, since it is smaller than the sum of its proper divisors (34791680).

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

21720832 is a wasteful number, since it uses less digits than its factorization.

21720832 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 94 (or 80 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 25.

The square root of 21720832 is about 4660.5613395813. The cubic root of 21720832 is about 279.0136725013.

The spelling of 21720832 in words is "twenty-one million, seven hundred twenty thousand, eight hundred thirty-two".