161905 has 4 divisors (see below), whose sum is σ = 194292. Its totient is φ = 129520.

The previous prime is 161881. The next prime is 161911. The reversal of 161905 is 509161.

161905 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 509161 = 227 ⋅2243.

It can be written as a sum of positive squares in 2 ways, for example, as 78961 + 82944 = 281^2 + 288^2 .

It is not a de Polignac number, because 161905 - 2⁵ = 161873 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 16186 + ... + 16195.

It is an arithmetic number, because the mean of its divisors is an integer number (48573).

2¹⁶¹⁹⁰⁵ is an apocalyptic number.

It is an amenable number.

161905 is a deficient number, since it is larger than the sum of its proper divisors (32387).

161905 is an equidigital number, since it uses as much as digits as its factorization.

161905 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32386.

The product of its (nonzero) digits is 270, while the sum is 22.

The square root of 161905 is about 402.3742039445. The cubic root of 161905 is about 54.5029597472.

The spelling of 161905 in words is "one hundred sixty-one thousand, nine hundred five".