21208536864 has 72 divisors (see below), whose sum is σ = 63859543020. Its totient is φ = 6653657088.

The previous prime is 21208536829. The next prime is 21208536887. The reversal of 21208536864 is 46863580212.

21208536864 is a `hidden beast` number, since 21 + 208 + 5 + 368 + 64 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 18034341264 + 3174195600 = 134292^2 + 56340^2 .

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

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 2161009 + ... + 2170800.

Almost surely, 2^21208536864 is an apocalyptic number.

21208536864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21208536864 is an abundant number, since it is smaller than the sum of its proper divisors (42651006156).

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

21208536864 is a wasteful number, since it uses less digits than its factorization.

21208536864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4331842 (or 4331831 counting only the distinct ones).

The product of its (nonzero) digits is 552960, while the sum is 45.

The spelling of 21208536864 in words is "twenty-one billion, two hundred eight million, five hundred thirty-six thousand, eight hundred sixty-four".