21558733721 has 8 divisors (see below), whose sum is σ = 24801723264. Its totient is φ = 18356536800.

The previous prime is 21558733717. The next prime is 21558733771. The reversal of 21558733721 is 12733785512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21558733721 - 2² = 21558733717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21558733711) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10197020 + ... + 10199133.

It is an arithmetic number, because the mean of its divisors is an integer number (3100215408).

Almost surely, 2^21558733721 is an apocalyptic number.

It is an amenable number.

21558733721 is a deficient number, since it is larger than the sum of its proper divisors (3242989543).

21558733721 is a wasteful number, since it uses less digits than its factorization.

21558733721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 20396311.

The product of its digits is 352800, while the sum is 44.

The spelling of 21558733721 in words is "twenty-one billion, five hundred fifty-eight million, seven hundred thirty-three thousand, seven hundred twenty-one".