166391 has 4 divisors (see below), whose sum is σ = 167352. Its totient is φ = 165432.

The previous prime is 166363. The next prime is 166393. The reversal of 166391 is 193661.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 193661 = 13 ⋅14897.

It is a cyclic number.

It is not a de Polignac number, because 166391 - 2¹⁰ = 165367 is a prime.

It is a Duffinian number.

It is a plaindrome in base 15.

It is a self number, because there is not a number n which added to its sum of digits gives 166391.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (166393) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 140 + ... + 593.

It is an arithmetic number, because the mean of its divisors is an integer number (41838).

166391 is a Friedman number, since it can be written as 16+(9*6+1)^3, using all its digits and the basic arithmetic operations.

2¹⁶⁶³⁹¹ is an apocalyptic number.

166391 is a deficient number, since it is larger than the sum of its proper divisors (961).

166391 is an equidigital number, since it uses as much as digits as its factorization.

166391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 960.

The product of its digits is 972, while the sum is 26.

The square root of 166391 is about 407.9105294057. The cubic root of 166391 is about 55.0017630289.

The spelling of 166391 in words is "one hundred sixty-six thousand, three hundred ninety-one".