21721800 has 96 divisors (see below), whose sum is σ = 69058080. Its totient is φ = 5644800.

The previous prime is 21721789. The next prime is 21721813. The reversal of 21721800 is 812712.

It is a zygodrome in base 9.

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, 24159 + ... + 25041.

It is an arithmetic number, because the mean of its divisors is an integer number (719355).

Almost surely, 2^21721800 is an apocalyptic number.

21721800 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 21721800, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (34529040).

21721800 is an abundant number, since it is smaller than the sum of its proper divisors (47336280).

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

21721800 is a wasteful number, since it uses less digits than its factorization.

21721800 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 943 (or 934 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 21.

The square root of 21721800 is about 4660.6651885756. The cubic root of 21721800 is about 279.0178172355.

The spelling of 21721800 in words is "twenty-one million, seven hundred twenty-one thousand, eight hundred".