21981100 has 72 divisors (see below), whose sum is σ = 52496640. Its totient is φ = 7951680.

The previous prime is 21981079. The next prime is 21981107. The reversal of 21981100 is 118912.

21981100 is nontrivially palindromic in base 9.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981107) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 43449 + ... + 43951.

It is an arithmetic number, because the mean of its divisors is an integer number (729120).

Almost surely, 2^21981100 is an apocalyptic number.

21981100 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 21981100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26248320).

21981100 is an abundant number, since it is smaller than the sum of its proper divisors (30515540).

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

21981100 is a wasteful number, since it uses less digits than its factorization.

21981100 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 559 (or 552 counting only the distinct ones).

The product of its (nonzero) digits is 144, while the sum is 22.

The square root of 21981100 is about 4688.4005801552. The cubic root of 21981100 is about 280.1236698595.

The spelling of 21981100 in words is "twenty-one million, nine hundred eighty-one thousand, one hundred".