161643991 has 4 divisors (see below), whose sum is σ = 162729000. Its totient is φ = 160558984.

The previous prime is 161643967. The next prime is 161643997. The reversal of 161643991 is 199346161.

It is a happy number.

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 161643991 - 2⁵ = 161643959 is a prime.

It is a super-2 number, since 2×161643991² = 52257559652816162, 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 (161643997) 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, 542281 + ... + 542578.

It is an arithmetic number, because the mean of its divisors is an integer number (40682250).

Almost surely, 2^161643991 is an apocalyptic number.

161643991 is a deficient number, since it is larger than the sum of its proper divisors (1085009).

161643991 is a wasteful number, since it uses less digits than its factorization.

161643991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1085008.

The product of its digits is 34992, while the sum is 40.

The square root of 161643991 is about 12713.9290150606. The cubic root of 161643991 is about 544.7365570190.

The spelling of 161643991 in words is "one hundred sixty-one million, six hundred forty-three thousand, nine hundred ninety-one".