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18391 = 53347

18391 has 4 divisors (see below), whose sum is σ = 18792. Its totient is φ = 17992.

The previous prime is 18379. The next prime is 18397. The reversal of 18391 is 19381.

18391 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2k-18391 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a plaindrome in base 11.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (18397) 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, 121 + ... + 226.

It is an arithmetic number, because the mean of its divisors is an integer number (4698).

218391 is an apocalyptic number.

18391 is a deficient number, since it is larger than the sum of its proper divisors (401).

18391 is an equidigital number, since it uses as much as digits as its factorization.

18391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 400.

The product of its digits is 216, while the sum is 22.

The square root of 18391 is about 135.6134211647. The cubic root of 18391 is about 26.3958173661.

Subtracting 18391 from its reverse (19381), we obtain a triangular number (990 = T44).

It can be divided in two parts, 183 and 91, that multiplied together give a triangular number (16653 = T182).

The spelling of 18391 in words is "eighteen thousand, three hundred ninety-one".

Divisors: 1 53 347 18391