168099991 has 4 divisors (see below), whose sum is σ = 172643272. Its totient is φ = 163556712.

The previous prime is 168099989. The next prime is 168100003. The reversal of 168099991 is 199990861.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199990861 = 7 ⋅28570123.

It is a cyclic number.

It is not a de Polignac number, because 168099991 - 2¹ = 168099989 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 (168099901) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2271585 + ... + 2271658.

It is an arithmetic number, because the mean of its divisors is an integer number (43160818).

Almost surely, 2^168099991 is an apocalyptic number.

168099991 is a deficient number, since it is larger than the sum of its proper divisors (4543281).

168099991 is an equidigital number, since it uses as much as digits as its factorization.

168099991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4543280.

The product of its (nonzero) digits is 314928, while the sum is 52.

The square root of 168099991 is about 12965.3380596111. The cubic root of 168099991 is about 551.8942848297.

It can be divided in two parts, 16809999 and 1, that added together give a square (16810000 = 4100²).

The spelling of 168099991 in words is "one hundred sixty-eight million, ninety-nine thousand, nine hundred ninety-one".