21005715456 has 288 divisors, whose sum is σ = 66595707360. Its totient is φ = 6325862400.

The previous prime is 21005715439. The next prime is 21005715461. The reversal of 21005715456 is 65451750012.

21005715456 is a `hidden beast` number, since 2 + 100 + 5 + 7 + 1 + 545 + 6 = 666.

It is a tau number, because it is divible by the number of its divisors (288).

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

It is a self number, because there is not a number n which added to its sum of digits gives 21005715456.

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, 63461211 + ... + 63461541.

It is an arithmetic number, because the mean of its divisors is an integer number (231235095).

Almost surely, 2^21005715456 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 21005715456, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33297853680).

21005715456 is an abundant number, since it is smaller than the sum of its proper divisors (45589991904).

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

21005715456 is a wasteful number, since it uses less digits than its factorization.

21005715456 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 683 (or 660 counting only the distinct ones).

The product of its (nonzero) digits is 42000, while the sum is 36.

The spelling of 21005715456 in words is "twenty-one billion, five million, seven hundred fifteen thousand, four hundred fifty-six".