21664688640 has 320 divisors, whose sum is σ = 81092309760. Its totient is φ = 4830658560.

The previous prime is 21664688629. The next prime is 21664688657. The reversal of 21664688640 is 4688646612.

It is a tau number, because it is divible by the number of its divisors (320).

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 2199246 + ... + 2209074.

It is an arithmetic number, because the mean of its divisors is an integer number (253413468).

Almost surely, 2^21664688640 is an apocalyptic number.

21664688640 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 21664688640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40546154880).

21664688640 is an abundant number, since it is smaller than the sum of its proper divisors (59427621120).

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

21664688640 is an equidigital number, since it uses as much as digits as its factorization.

21664688640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9903 (or 9887 counting only the distinct ones).

The product of its (nonzero) digits is 2654208, while the sum is 51.

The spelling of 21664688640 in words is "twenty-one billion, six hundred sixty-four million, six hundred eighty-eight thousand, six hundred forty".