21643356720 has 80 divisors (see below), whose sum is σ = 67183601760. Its totient is φ = 5763889152.

The previous prime is 21643356689. The next prime is 21643356737. The reversal of 21643356720 is 2765334612.

It is a tau number, because it is divible by the number of its divisors (80).

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 122116 + ... + 241244.

It is an arithmetic number, because the mean of its divisors is an integer number (839795022).

Almost surely, 2^21643356720 is an apocalyptic number.

21643356720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21643356720 is an abundant number, since it is smaller than the sum of its proper divisors (45540245040).

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

21643356720 is a wasteful number, since it uses less digits than its factorization.

21643356720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 119902 (or 119896 counting only the distinct ones).

The product of its (nonzero) digits is 181440, while the sum is 39.

The spelling of 21643356720 in words is "twenty-one billion, six hundred forty-three million, three hundred fifty-six thousand, seven hundred twenty".