81381 has 4 divisors (see below), whose sum is σ = 108512. Its totient is φ = 54252.

The previous prime is 81373. The next prime is 81401. The reversal of 81381 is 18318.

It is a happy number.

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 not a de Polignac number, because 81381 - 2³ = 81373 is a prime.

It is a super-2 number, since 2×81381² = 13245734322, which contains 22 as substring.

It is a D-number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81331) 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, 13561 + ... + 13566.

It is an arithmetic number, because the mean of its divisors is an integer number (27128).

2⁸¹³⁸¹ is an apocalyptic number.

It is an amenable number.

81381 is a deficient number, since it is larger than the sum of its proper divisors (27131).

81381 is a wasteful number, since it uses less digits than its factorization.

81381 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 27130.

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

The square root of 81381 is about 285.2735529277. The cubic root of 81381 is about 43.3352201677.

Adding to 81381 its reverse (18318), we get a palindrome (99699).

The spelling of 81381 in words is "eighty-one thousand, three hundred eighty-one".