21331872 has 72 divisors (see below), whose sum is σ = 64245636. Its totient is φ = 6690816.

The previous prime is 21331867. The next prime is 21331873. The reversal of 21331872 is 27813312.

It can be written as a sum of positive squares in 2 ways, for example, as 15968016 + 5363856 = 3996^2 + 2316^2 .

It is a tau number, because it is divible by the number of its divisors (72).

It is not an unprimeable number, because it can be changed into a prime (21331873) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2718 + ... + 7074.

Almost surely, 2^21331872 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 21331872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32122818).

21331872 is an abundant number, since it is smaller than the sum of its proper divisors (42913764).

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

21331872 is a wasteful number, since it uses less digits than its factorization.

21331872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4390 (or 4379 counting only the distinct ones).

The product of its digits is 2016, while the sum is 27.

The square root of 21331872 is about 4618.6439568341. The cubic root of 21331872 is about 277.3381768960.

It can be divided in two parts, 2133 and 1872, that added together give a triangular number (4005 = T₈₉).

The spelling of 21331872 in words is "twenty-one million, three hundred thirty-one thousand, eight hundred seventy-two".