81591 has 4 divisors (see below), whose sum is σ = 108792. Its totient is φ = 54392.

The previous prime is 81569. The next prime is 81611. The reversal of 81591 is 19518.

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

It is a cyclic number.

It is not a de Polignac number, because 81591 - 2⁵ = 81559 is a prime.

It is a D-number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81551) 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, 13596 + ... + 13601.

It is an arithmetic number, because the mean of its divisors is an integer number (27198).

2⁸¹⁵⁹¹ is an apocalyptic number.

81591 is a deficient number, since it is larger than the sum of its proper divisors (27201).

81591 is a wasteful number, since it uses less digits than its factorization.

81591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27200.

The product of its digits is 360, while the sum is 24.

The square root of 81591 is about 285.6413835564. The cubic root of 81591 is about 43.3724630119.

The spelling of 81591 in words is "eighty-one thousand, five hundred ninety-one".