165911381891 has 4 divisors (see below), whose sum is σ = 171263361984. Its totient is φ = 160559401800.

The previous prime is 165911381887. The next prime is 165911381897. The reversal of 165911381891 is 198183119561.

It is a happy number.

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

It is a cyclic number.

It is not a de Polignac number, because 165911381891 - 2² = 165911381887 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (165911381897) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2675990000 + ... + 2675990061.

It is an arithmetic number, because the mean of its divisors is an integer number (42815840496).

Almost surely, 2^165911381891 is an apocalyptic number.

165911381891 is a deficient number, since it is larger than the sum of its proper divisors (5351980093).

165911381891 is an equidigital number, since it uses as much as digits as its factorization.

165911381891 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5351980092.

The product of its digits is 466560, while the sum is 53.

The spelling of 165911381891 in words is "one hundred sixty-five billion, nine hundred eleven million, three hundred eighty-one thousand, eight hundred ninety-one".