21189108565 has 4 divisors (see below), whose sum is σ = 25426930284. Its totient is φ = 16951286848.

The previous prime is 21189108557. The next prime is 21189108569. The reversal of 21189108565 is 56580198112.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 2787100849 + 18402007716 = 52793^2 + 135654^2 .

It is a cyclic number.

It is not a de Polignac number, because 21189108565 - 2³ = 21189108557 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21189108569) 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 3 ways as a sum of consecutive naturals, for example, 2118910852 + ... + 2118910861.

It is an arithmetic number, because the mean of its divisors is an integer number (6356732571).

Almost surely, 2^21189108565 is an apocalyptic number.

It is an amenable number.

21189108565 is a deficient number, since it is larger than the sum of its proper divisors (4237821719).

21189108565 is an equidigital number, since it uses as much as digits as its factorization.

21189108565 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4237821718.

The product of its (nonzero) digits is 172800, while the sum is 46.

The spelling of 21189108565 in words is "twenty-one billion, one hundred eighty-nine million, one hundred eight thousand, five hundred sixty-five".