161991955 has 4 divisors (see below), whose sum is σ = 194390352. Its totient is φ = 129593560.

The previous prime is 161991937. The next prime is 161991971. The reversal of 161991955 is 559199161.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 161991955 - 2⁹ = 161991443 is a prime.

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, 16199191 + ... + 16199200.

It is an arithmetic number, because the mean of its divisors is an integer number (48597588).

Almost surely, 2^161991955 is an apocalyptic number.

161991955 is a deficient number, since it is larger than the sum of its proper divisors (32398397).

161991955 is an equidigital number, since it uses as much as digits as its factorization.

161991955 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 32398396.

The product of its digits is 109350, while the sum is 46.

The square root of 161991955 is about 12727.6060199866. The cubic root of 161991955 is about 545.1271537897.

The spelling of 161991955 in words is "one hundred sixty-one million, nine hundred ninety-one thousand, nine hundred fifty-five".