81581 has 4 divisors (see below), whose sum is σ = 85152. Its totient is φ = 78012.

The previous prime is 81569. The next prime is 81611. The reversal of 81581 is 18518.

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 a cyclic number.

It is not a de Polignac number, because 81581 - 2⁶ = 81517 is a prime.

It is a super-2 number, since 2×81581² = 13310919122, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (23), and also a Moran number because the ratio is a prime number: 3547 = 81581 / (8 + 1 + 5 + 8 + 1).

It is a Duffinian 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 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, 1751 + ... + 1796.

It is an arithmetic number, because the mean of its divisors is an integer number (21288).

2⁸¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

81581 is a deficient number, since it is larger than the sum of its proper divisors (3571).

81581 is a wasteful number, since it uses less digits than its factorization.

81581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3570.

The product of its digits is 320, while the sum is 23.

The square root of 81581 is about 285.6238785536. The cubic root of 81581 is about 43.3706909931.

The spelling of 81581 in words is "eighty-one thousand, five hundred eighty-one".