31681 has 4 divisors (see below), whose sum is σ = 34132. Its totient is φ = 29232.

The previous prime is 31667. The next prime is 31687. The reversal of 31681 is 18613.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18613 = 7 ⋅2659.

It can be written as a sum of positive squares in 2 ways, for example, as 18225 + 13456 = 135^2 + 116^2 .

It is a cyclic number.

It is not a de Polignac number, because 31681 - 2⁵ = 31649 is a prime.

It is a super-2 number, since 2×31681² = 2007371522, which contains 22 as substring.

It is a Duffinian number.

31681 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (31687) 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, 1206 + ... + 1231.

It is an arithmetic number, because the mean of its divisors is an integer number (8533).

2³¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

31681 is a deficient number, since it is larger than the sum of its proper divisors (2451).

31681 is a wasteful number, since it uses less digits than its factorization.

31681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2450.

The product of its digits is 144, while the sum is 19.

The square root of 31681 is about 177.9915728342. The cubic root of 31681 is about 31.6421725022.

The spelling of 31681 in words is "thirty-one thousand, six hundred eighty-one".