21981358728 has 96 divisors (see below), whose sum is σ = 70232348160. Its totient is φ = 6077790720.

The previous prime is 21981358687. The next prime is 21981358747. The reversal of 21981358728 is 82785318912.

21981358728 is a `hidden beast` number, since 21 + 9 + 8 + 13 + 587 + 28 = 666.

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, 687825 + ... + 719072.

It is an arithmetic number, because the mean of its divisors is an integer number (731586960).

Almost surely, 2^21981358728 is an apocalyptic number.

21981358728 is a gapful number since it is divisible by the number (28) formed by its first and last digit.

It is an amenable number.

21981358728 is an abundant number, since it is smaller than the sum of its proper divisors (48250989432).

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

21981358728 is a wasteful number, since it uses less digits than its factorization.

21981358728 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1406947 (or 1406940 counting only the distinct ones).

The product of its digits is 1935360, while the sum is 54.

The spelling of 21981358728 in words is "twenty-one billion, nine hundred eighty-one million, three hundred fifty-eight thousand, seven hundred twenty-eight".