81881 has 4 divisors (see below), whose sum is σ = 84132. Its totient is φ = 79632.

The previous prime is 81869. The next prime is 81883. The reversal of 81881 is 18818.

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

It can be written as a sum of positive squares in 2 ways, for example, as 78400 + 3481 = 280^2 + 59^2 .

It is a cyclic number.

It is not a de Polignac number, because 81881 - 2⁶ = 81817 is a prime.

It is a super-2 number, since 2×81881² = 13408996322, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81881.

It is not an unprimeable number, because it can be changed into a prime (81883) 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, 1070 + ... + 1143.

It is an arithmetic number, because the mean of its divisors is an integer number (21033).

2⁸¹⁸⁸¹ is an apocalyptic number.

It is an amenable number.

81881 is a deficient number, since it is larger than the sum of its proper divisors (2251).

81881 is a wasteful number, since it uses less digits than its factorization.

81881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2250.

The product of its digits is 512, while the sum is 26.

The square root of 81881 is about 286.1485628131. The cubic root of 81881 is about 43.4237886955.

The spelling of 81881 in words is "eighty-one thousand, eight hundred eighty-one".