165840391 has 4 divisors (see below), whose sum is σ = 167838552. Its totient is φ = 163842232.

The previous prime is 165840371. The next prime is 165840397. The reversal of 165840391 is 193048561.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 193048561 = 163 ⋅1184347.

It is a cyclic number.

It is not a de Polignac number, because 165840391 - 2¹⁹ = 165316103 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 165840391.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (165840397) 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, 998956 + ... + 999121.

It is an arithmetic number, because the mean of its divisors is an integer number (41959638).

Almost surely, 2^165840391 is an apocalyptic number.

165840391 is a deficient number, since it is larger than the sum of its proper divisors (1998161).

165840391 is an equidigital number, since it uses as much as digits as its factorization.

165840391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1998160.

The product of its (nonzero) digits is 25920, while the sum is 37.

The square root of 165840391 is about 12877.9032066560. The cubic root of 165840391 is about 549.4102670633.

The spelling of 165840391 in words is "one hundred sixty-five million, eight hundred forty thousand, three hundred ninety-one".