81911 has 4 divisors (see below), whose sum is σ = 82824. Its totient is φ = 81000.

The previous prime is 81901. The next prime is 81919. The reversal of 81911 is 11918.

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.

It is a cyclic number.

It is not a de Polignac number, because 81911 - 2⁶ = 81847 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81919) 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, 305 + ... + 506.

It is an arithmetic number, because the mean of its divisors is an integer number (20706).

2⁸¹⁹¹¹ is an apocalyptic number.

81911 is a deficient number, since it is larger than the sum of its proper divisors (913).

81911 is a wasteful number, since it uses less digits than its factorization.

81911 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 912.

The product of its digits is 72, while the sum is 20.

The square root of 81911 is about 286.2009783352. The cubic root of 81911 is about 43.4290913282.

It can be divided in two parts, 8191 and 1, that added together give a 13-th power (8192 = 2¹³).

The spelling of 81911 in words is "eighty-one thousand, nine hundred eleven".