21881351808 has 96 divisors (see below), whose sum is σ = 63054203940. Its totient is φ = 7283552256.

The previous prime is 21881351777. The next prime is 21881351809. The reversal of 21881351808 is 80815318812.

21881351808 is a `hidden beast` number, since 218 + 8 + 1 + 351 + 80 + 8 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 18931558464 + 2949793344 = 137592^2 + 54312^2 .

It is a tau number, because it is divible by the number of its divisors (96).

It is not an unprimeable number, because it can be changed into a prime (21881351809) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 831460 + ... + 857372.

Almost surely, 2^21881351808 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 21881351808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31527101970).

21881351808 is an abundant number, since it is smaller than the sum of its proper divisors (41172852132).

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

21881351808 is a wasteful number, since it uses less digits than its factorization.

21881351808 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 26666 (or 26651 counting only the distinct ones).

The product of its (nonzero) digits is 122880, while the sum is 45.

The spelling of 21881351808 in words is "twenty-one billion, eight hundred eighty-one million, three hundred fifty-one thousand, eight hundred eight".