161091809 has 2 divisors, whose sum is σ = 161091810. Its totient is φ = 161091808.

The previous prime is 161091787. The next prime is 161091811. The reversal of 161091809 is 908190161.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 147379600 + 13712209 = 12140^2 + 3703^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-161091809 is a prime.

It is a Sophie Germain prime.

Together with 161091811, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (161091109) 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 as a sum of consecutive naturals, namely, 80545904 + 80545905.

It is an arithmetic number, because the mean of its divisors is an integer number (80545905).

Almost surely, 2^161091809 is an apocalyptic number.

It is an amenable number.

161091809 is a deficient number, since it is larger than the sum of its proper divisors (1).

161091809 is an equidigital number, since it uses as much as digits as its factorization.

161091809 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3888, while the sum is 35.

The square root of 161091809 is about 12692.1948062579. The cubic root of 161091809 is about 544.1155691333.

The spelling of 161091809 in words is "one hundred sixty-one million, ninety-one thousand, eight hundred nine".