21705721608 has 64 divisors (see below), whose sum is σ = 57206661120. Its totient is φ = 6852859200.

The previous prime is 21705721607. The next prime is 21705721663. The reversal of 21705721608 is 80612750712.

It is a super-2 number, since 2×21705721608² (a number of 21 digits) contains 22 as substring.

It is a hoax number, since the sum of its digits (39) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21705721607) by changing a digit.

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, 275398 + ... + 345333.

It is an arithmetic number, because the mean of its divisors is an integer number (893854080).

Almost surely, 2^21705721608 is an apocalyptic number.

It is an amenable number.

21705721608 is an abundant number, since it is smaller than the sum of its proper divisors (35500939512).

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

21705721608 is a wasteful number, since it uses less digits than its factorization.

21705721608 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 620818 (or 620814 counting only the distinct ones).

The product of its (nonzero) digits is 47040, while the sum is 39.

The spelling of 21705721608 in words is "twenty-one billion, seven hundred five million, seven hundred twenty-one thousand, six hundred eight".