21981328 has 20 divisors (see below), whose sum is σ = 44830960. Its totient is φ = 10412064.

The previous prime is 21981319. The next prime is 21981329. The reversal of 21981328 is 82318912.

It is a junction number, because it is equal to n+sod(n) for n = 21981293 and 21981302.

It is not an unprimeable number, because it can be changed into a prime (21981329) 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 3 ways as a sum of consecutive naturals, for example, 35850 + ... + 36457.

It is an arithmetic number, because the mean of its divisors is an integer number (2241548).

Almost surely, 2^21981328 is an apocalyptic number.

It is an amenable number.

21981328 is an abundant number, since it is smaller than the sum of its proper divisors (22849632).

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

21981328 is a wasteful number, since it uses less digits than its factorization.

21981328 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 72334 (or 72328 counting only the distinct ones).

The product of its digits is 6912, while the sum is 34.

The square root of 21981328 is about 4688.4248954206. The cubic root of 21981328 is about 280.1246383881.

The spelling of 21981328 in words is "twenty-one million, nine hundred eighty-one thousand, three hundred twenty-eight".