161991143 has 4 divisors (see below), whose sum is σ = 166369320. Its totient is φ = 157612968.

The previous prime is 161991119. The next prime is 161991157. The reversal of 161991143 is 341199161.

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

It is a cyclic number.

It is not a de Polignac number, because 161991143 - 2¹⁰ = 161990119 is a prime.

It is a super-2 number, since 2×161991143² = 52482260820892898, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (161991103) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2189033 + ... + 2189106.

It is an arithmetic number, because the mean of its divisors is an integer number (41592330).

Almost surely, 2^161991143 is an apocalyptic number.

161991143 is a deficient number, since it is larger than the sum of its proper divisors (4378177).

161991143 is an equidigital number, since it uses as much as digits as its factorization.

161991143 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4378176.

The product of its digits is 5832, while the sum is 35.

The square root of 161991143 is about 12727.5741207820. The cubic root of 161991143 is about 545.1262429543.

The spelling of 161991143 in words is "one hundred sixty-one million, nine hundred ninety-one thousand, one hundred forty-three".