21209806800 has 720 divisors, whose sum is σ = 94602070080. Its totient is φ = 4473584640.

The previous prime is 21209806789. The next prime is 21209806817. The reversal of 21209806800 is 860890212.

It is a tau number, because it is divible by the number of its divisors (720).

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

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 6878059 + ... + 6881141.

It is an arithmetic number, because the mean of its divisors is an integer number (131391764).

Almost surely, 2^21209806800 is an apocalyptic number.

21209806800 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 21209806800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (47301035040).

21209806800 is an abundant number, since it is smaller than the sum of its proper divisors (73392263280).

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

21209806800 is a wasteful number, since it uses less digits than its factorization.

21209806800 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3137 (or 3113 counting only the distinct ones).

The product of its (nonzero) digits is 13824, while the sum is 36.

The spelling of 21209806800 in words is "twenty-one billion, two hundred nine million, eight hundred six thousand, eight hundred".