21161521566 has 32 divisors (see below), whose sum is σ = 47307214080. Its totient is φ = 7011598968.

The previous prime is 21161521559. The next prime is 21161521571. The reversal of 21161521566 is 66512516112.

21161521566 is a `hidden beast` number, since 2 + 11 + 61 + 5 + 21 + 566 = 666.

It is a self number, because there is not a number n which added to its sum of digits gives 21161521566.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 1164276 + ... + 1182311.

It is an arithmetic number, because the mean of its divisors is an integer number (1478350440).

Almost surely, 2^21161521566 is an apocalyptic number.

21161521566 is an abundant number, since it is smaller than the sum of its proper divisors (26145692514).

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

21161521566 is a wasteful number, since it uses less digits than its factorization.

21161521566 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2346765 (or 2346759 counting only the distinct ones).

The product of its digits is 21600, while the sum is 36.

The spelling of 21161521566 in words is "twenty-one billion, one hundred sixty-one million, five hundred twenty-one thousand, five hundred sixty-six".