21205621720 has 32 divisors (see below), whose sum is σ = 48060928800. Its totient is φ = 8420332288.

The previous prime is 21205621681. The next prime is 21205621771. The reversal of 21205621720 is 2712650212.

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, 1929340 + ... + 1940299.

It is an arithmetic number, because the mean of its divisors is an integer number (1501904025).

Almost surely, 2^21205621720 is an apocalyptic number.

21205621720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21205621720 is an abundant number, since it is smaller than the sum of its proper divisors (26855307080).

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

21205621720 is a wasteful number, since it uses less digits than its factorization.

21205621720 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3869787 (or 3869783 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 28.

The spelling of 21205621720 in words is "twenty-one billion, two hundred five million, six hundred twenty-one thousand, seven hundred twenty".