31581 has 18 divisors (see below), whose sum is σ = 51870. Its totient is φ = 18480.

The previous prime is 31573. The next prime is 31583. The reversal of 31581 is 18513.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 27225 + 4356 = 165^2 + 66^2 .

It is not a de Polignac number, because 31581 - 2³ = 31573 is a prime.

It is a super-2 number, since 2×31581² = 1994719122, which contains 22 as substring.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 31581.

It is not an unprimeable number, because it can be changed into a prime (31583) 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 17 ways as a sum of consecutive naturals, for example, 1075 + ... + 1103.

2³¹⁵⁸¹ is an apocalyptic number.

It is an amenable number.

31581 is a deficient number, since it is larger than the sum of its proper divisors (20289).

31581 is a wasteful number, since it uses less digits than its factorization.

31581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57 (or 43 counting only the distinct ones).

The product of its digits is 120, while the sum is 18.

The square root of 31581 is about 177.7104386354. The cubic root of 31581 is about 31.6088449310.

The spelling of 31581 in words is "thirty-one thousand, five hundred eighty-one".