91681 has 4 divisors (see below), whose sum is σ = 97092. Its totient is φ = 86272.

The previous prime is 91673. The next prime is 91691. The reversal of 91681 is 18619.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18619 = 43 ⋅433.

It can be written as a sum of positive squares in 2 ways, for example, as 80656 + 11025 = 284^2 + 105^2 .

It is a cyclic number.

It is not a de Polignac number, because 91681 - 2³ = 91673 is a prime.

It is a super-2 number, since 2×91681² = 16810811522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (91621) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2680 + ... + 2713.

It is an arithmetic number, because the mean of its divisors is an integer number (24273).

2⁹¹⁶⁸¹ is an apocalyptic number.

91681 is the 192-nd centered pentagonal number.

It is an amenable number.

91681 is a deficient number, since it is larger than the sum of its proper divisors (5411).

91681 is a wasteful number, since it uses less digits than its factorization.

91681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5410.

The product of its digits is 432, while the sum is 25.

The square root of 91681 is about 302.7887052055. The cubic root of 91681 is about 45.0913371201.

It can be divided in two parts, 9 and 1681, that multiplied together give a square (15129 = 123²).

The spelling of 91681 in words is "ninety-one thousand, six hundred eighty-one".