21568920561 has 48 divisors (see below), whose sum is σ = 34174333440. Its totient is φ = 13049786880.

The previous prime is 21568920559. The next prime is 21568920613. The reversal of 21568920561 is 16502986512.

21568920561 is a `hidden beast` number, since 2 + 1 + 5 + 6 + 89 + 2 + 0 + 561 = 666.

It is not a de Polignac number, because 21568920561 - 2¹ = 21568920559 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21568920161) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 1334235 + ... + 1350303.

It is an arithmetic number, because the mean of its divisors is an integer number (711965280).

Almost surely, 2^21568920561 is an apocalyptic number.

It is an amenable number.

21568920561 is a deficient number, since it is larger than the sum of its proper divisors (12605412879).

21568920561 is a wasteful number, since it uses less digits than its factorization.

21568920561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16406 (or 16403 counting only the distinct ones).

The product of its (nonzero) digits is 259200, while the sum is 45.

The spelling of 21568920561 in words is "twenty-one billion, five hundred sixty-eight million, nine hundred twenty thousand, five hundred sixty-one".