21721958664 has 128 divisors (see below), whose sum is σ = 64297082880. Its totient is φ = 5984294400.

The previous prime is 21721958627. The next prime is 21721958683. The reversal of 21721958664 is 46685912712.

It is a Smith number, since the sum of its digits (51) coincides with the sum of the digits of its prime factors.

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, 1456027 + ... + 1470869.

It is an arithmetic number, because the mean of its divisors is an integer number (502320960).

Almost surely, 2^21721958664 is an apocalyptic number.

21721958664 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 21721958664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32148541440).

21721958664 is an abundant number, since it is smaller than the sum of its proper divisors (42575124216).

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

21721958664 is a wasteful number, since it uses less digits than its factorization.

21721958664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15171 (or 15167 counting only the distinct ones).

The product of its digits is 1451520, while the sum is 51.

The spelling of 21721958664 in words is "twenty-one billion, seven hundred twenty-one million, nine hundred fifty-eight thousand, six hundred sixty-four".