81681 has 8 divisors (see below), whose sum is σ = 114720. Its totient is φ = 51552.

The previous prime is 81677. The next prime is 81689. The reversal of 81681 is 18618.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81681 - 2² = 81677 is a prime.

It is a super-2 number, since 2×81681² = 13343571522, which contains 22 as substring.

It is a Smith number, since the sum of its digits (24) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81689) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 660 + ... + 773.

It is an arithmetic number, because the mean of its divisors is an integer number (14340).

2⁸¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

81681 is a deficient number, since it is larger than the sum of its proper divisors (33039).

81681 is a wasteful number, since it uses less digits than its factorization.

81681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1455.

The product of its digits is 384, while the sum is 24.

The square root of 81681 is about 285.7988803337. The cubic root of 81681 is about 43.3884046692.

The spelling of 81681 in words is "eighty-one thousand, six hundred eighty-one".