161209 has 4 divisors (see below), whose sum is σ = 165604. Its totient is φ = 156816.

The previous prime is 161201. The next prime is 161221. The reversal of 161209 is 902161.

161209 = 5² + 6² + ... + 78².

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 156025 + 5184 = 395^2 + 72^2 .

It is a cyclic number.

It is not a de Polignac number, because 161209 - 2³ = 161201 is a prime.

It is a Duffinian number.

161209 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (161201) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2142 + ... + 2215.

It is an arithmetic number, because the mean of its divisors is an integer number (41401).

2¹⁶¹²⁰⁹ is an apocalyptic number.

It is an amenable number.

161209 is a deficient number, since it is larger than the sum of its proper divisors (4395).

161209 is an equidigital number, since it uses as much as digits as its factorization.

161209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4394.

The product of its (nonzero) digits is 108, while the sum is 19.

The square root of 161209 is about 401.5084058896. The cubic root of 161209 is about 54.4247481471.

It can be divided in two parts, 16120 and 9, that added together give a square (16129 = 127²).

The spelling of 161209 in words is "one hundred sixty-one thousand, two hundred nine".