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18381 = 311557

18381 has 8 divisors (see below), whose sum is σ = 26784. Its totient is φ = 11120.

The previous prime is 18379. The next prime is 18397.

It is a happy number.

18381 is nontrivially palindromic in base 10.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 18381 - 21 = 18379 is a prime.

It is a super-2 number, since 2×183812 = 675722322, which contains 22 as substring.

It is an Ulam number.

It is an alternating number because its digits alternate between odd and even.

18381 is a lucky number.

It is a plaindrome in base 14 and base 16.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 18381.

It is not an unprimeable number, because it can be changed into a prime (18301) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 246 + ... + 311.

It is an arithmetic number, because the mean of its divisors is an integer number (3348).

218381 is an apocalyptic number.

18381 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

18381 is a deficient number, since it is larger than the sum of its proper divisors (8403).

18381 is a wasteful number, since it uses less digits than its factorization.

18381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 571.

The product of its digits is 192, while the sum is 21.

The square root of 18381 is about 135.5765466443. The cubic root of 18381 is about 26.3910323077.

The spelling of 18381 in words is "eighteen thousand, three hundred eighty-one".

Divisors: 1 3 11 33 557 1671 6127 18381