161991913 has 4 divisors (see below), whose sum is σ = 162189568. Its totient is φ = 161794260.

The previous prime is 161991899. The next prime is 161991919. The reversal of 161991913 is 319199161.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 161991913 - 2⁵ = 161991881 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (161991919) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 97593 + ... + 99238.

It is an arithmetic number, because the mean of its divisors is an integer number (40547392).

Almost surely, 2^161991913 is an apocalyptic number.

It is an amenable number.

161991913 is a deficient number, since it is larger than the sum of its proper divisors (197655).

161991913 is an equidigital number, since it uses as much as digits as its factorization.

161991913 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 197654.

The product of its digits is 13122, while the sum is 40.

The square root of 161991913 is about 12727.6043700297. The cubic root of 161991913 is about 545.1271066776.

The spelling of 161991913 in words is "one hundred sixty-one million, nine hundred ninety-one thousand, nine hundred thirteen".