21097721920 has 56 divisors (see below), whose sum is σ = 54806136768. Its totient is φ = 7671897600.

The previous prime is 21097721899. The next prime is 21097721989. The reversal of 21097721920 is 2912779012.

It is a super-2 number, since 2×21097721920² (a number of 21 digits) contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (40).

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 7 ways as a sum of consecutive naturals, for example, 2993316 + ... + 3000355.

Almost surely, 2^21097721920 is an apocalyptic number.

21097721920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21097721920 is an abundant number, since it is smaller than the sum of its proper divisors (33708414848).

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

21097721920 is a wasteful number, since it uses less digits than its factorization.

21097721920 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5993699 (or 5993689 counting only the distinct ones).

The product of its (nonzero) digits is 31752, while the sum is 40.

The spelling of 21097721920 in words is "twenty-one billion, ninety-seven million, seven hundred twenty-one thousand, nine hundred twenty".