21539909664 has 384 divisors, whose sum is σ = 81398016000. Its totient is φ = 5381489664.

The previous prime is 21539909627. The next prime is 21539909717. The reversal of 21539909664 is 46690993512.

It is a Harshad number since it is a multiple of its sum of digits (54).

It is a self number, because there is not a number n which added to its sum of digits gives 21539909664.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 1486647 + ... + 1501065.

It is an arithmetic number, because the mean of its divisors is an integer number (211974000).

Almost surely, 2^21539909664 is an apocalyptic number.

21539909664 is a gapful number since it is divisible by the number (24) 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 21539909664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40699008000).

21539909664 is an abundant number, since it is smaller than the sum of its proper divisors (59858106336).

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

21539909664 is a wasteful number, since it uses less digits than its factorization.

21539909664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14477 (or 14463 counting only the distinct ones).

The product of its (nonzero) digits is 3149280, while the sum is 54.

The spelling of 21539909664 in words is "twenty-one billion, five hundred thirty-nine million, nine hundred nine thousand, six hundred sixty-four".