21815981100 has 324 divisors, whose sum is σ = 72828989688. Its totient is φ = 5668704000.

The previous prime is 21815981081. The next prime is 21815981129. The reversal of 21815981100 is 118951812.

It is a tau number, because it is divible by the number of its divisors (324).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 107 ways as a sum of consecutive naturals, for example, 26899695 + ... + 26900505.

Almost surely, 2^21815981100 is an apocalyptic number.

21815981100 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21815981100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36414494844).

21815981100 is an abundant number, since it is smaller than the sum of its proper divisors (51013008588).

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

21815981100 is an equidigital number, since it uses as much as digits as its factorization.

21815981100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 890 (or 862 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 36.

The spelling of 21815981100 in words is "twenty-one billion, eight hundred fifteen million, nine hundred eighty-one thousand, one hundred".