21558864672 has 72 divisors (see below), whose sum is σ = 64534775760. Its totient is φ = 6808060800.

The previous prime is 21558864637. The next prime is 21558864673. The reversal of 21558864672 is 27646885512.

21558864672 is a `hidden beast` number, since 2 + 1 + 558 + 86 + 4 + 6 + 7 + 2 = 666.

It is a tau number, because it is divible by the number of its divisors (72).

It is not an unprimeable number, because it can be changed into a prime (21558864673) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 1964454 + ... + 1975397.

It is an arithmetic number, because the mean of its divisors is an integer number (896316330).

Almost surely, 2^21558864672 is an apocalyptic number.

It is an amenable number.

21558864672 is an abundant number, since it is smaller than the sum of its proper divisors (42975911088).

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

21558864672 is a wasteful number, since it uses less digits than its factorization.

21558864672 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3939886 (or 3939875 counting only the distinct ones).

The product of its digits is 6451200, while the sum is 54.

The spelling of 21558864672 in words is "twenty-one billion, five hundred fifty-eight million, eight hundred sixty-four thousand, six hundred seventy-two".