163991791681 has 3 divisors (see below), whose sum is σ = 163992196641. Its totient is φ = 163991386722.

The previous prime is 163991791661. The next prime is 163991791693. The reversal of 163991791681 is 186197199361.

The square root of 163991791681 is 404959.

It is a perfect power (a square), and thus also a powerful number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 163991791681 - 2⁹ = 163991791169 is a prime.

It is a super-2 number, since 2×163991791681² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (163991791661) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 202480 + ... + 607438.

It is an arithmetic number, because the mean of its divisors is an integer number (54664065547).

Almost surely, 2^163991791681 is an apocalyptic number.

163991791681 is the 404959-th square number.

163991791681 is the 202480-th centered octagonal number.

It is an amenable number.

163991791681 is a deficient number, since it is larger than the sum of its proper divisors (404960).

163991791681 is an frugal number, since it uses more digits than its factorization.

163991791681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 809918 (or 404959 counting only the distinct ones).

The product of its digits is 4408992, while the sum is 61.

The spelling of 163991791681 in words is "one hundred sixty-three billion, nine hundred ninety-one million, seven hundred ninety-one thousand, six hundred eighty-one".