21801720724 has 48 divisors (see below), whose sum is σ = 44562672000. Its totient is φ = 9329029248.

The previous prime is 21801720697. The next prime is 21801720727. The reversal of 21801720724 is 42702710812.

It is a happy number.

It is a self number, because there is not a number n which added to its sum of digits gives 21801720724.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21801720727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 892092 + ... + 916204.

It is an arithmetic number, because the mean of its divisors is an integer number (928389000).

Almost surely, 2^21801720724 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 21801720724, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22281336000).

21801720724 is an abundant number, since it is smaller than the sum of its proper divisors (22760951276).

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

21801720724 is a wasteful number, since it uses less digits than its factorization.

21801720724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24797 (or 24781 counting only the distinct ones).

The product of its (nonzero) digits is 12544, while the sum is 34.

The spelling of 21801720724 in words is "twenty-one billion, eight hundred one million, seven hundred twenty thousand, seven hundred twenty-four".