21605305664 has 56 divisors (see below), whose sum is σ = 44283782400. Its totient is φ = 10447626240.

The previous prime is 21605305649. The next prime is 21605305693. The reversal of 21605305664 is 46650350612.

It is a happy number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5035232 + ... + 5039520.

Almost surely, 2^21605305664 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 21605305664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22141891200).

21605305664 is an abundant number, since it is smaller than the sum of its proper divisors (22678476736).

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

21605305664 is a wasteful number, since it uses less digits than its factorization.

21605305664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6871 (or 6861 counting only the distinct ones).

The product of its (nonzero) digits is 129600, while the sum is 38.

The spelling of 21605305664 in words is "twenty-one billion, six hundred five million, three hundred five thousand, six hundred sixty-four".