21715787520 has 432 divisors, whose sum is σ = 87505209792. Its totient is φ = 4868997120.

The previous prime is 21715787491. The next prime is 21715787647. The reversal of 21715787520 is 2578751712.

21715787520 is a `hidden beast` number, since 2 + 1 + 7 + 1 + 578 + 75 + 2 + 0 = 666.

It is a super-2 number, since 2×21715787520² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 4271380 + ... + 4276460.

It is an arithmetic number, because the mean of its divisors is an integer number (202558356).

Almost surely, 2^21715787520 is an apocalyptic number.

21715787520 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 21715787520, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (43752604896).

21715787520 is an abundant number, since it is smaller than the sum of its proper divisors (65789422272).

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

21715787520 is a wasteful number, since it uses less digits than its factorization.

21715787520 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5168 (or 5151 counting only the distinct ones).

The product of its (nonzero) digits is 274400, while the sum is 45.

The spelling of 21715787520 in words is "twenty-one billion, seven hundred fifteen million, seven hundred eighty-seven thousand, five hundred twenty".