13581 has 8 divisors (see below), whose sum is σ = 20160. Its totient is φ = 9036.

The previous prime is 13577. The next prime is 13591. The reversal of 13581 is 18531.

It is a happy number.

13581 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 13581 - 2² = 13577 is a prime.

It is a super-2 number, since 2×13581² = 368887122, which contains 22 as substring.

13581 is a lucky number.

It is a nialpdrome in base 7.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (13591) 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 7 ways as a sum of consecutive naturals, for example, 225 + ... + 278.

It is an arithmetic number, because the mean of its divisors is an integer number (2520).

2¹³⁵⁸¹ is an apocalyptic number.

It is an amenable number.

13581 is a deficient number, since it is larger than the sum of its proper divisors (6579).

13581 is an equidigital number, since it uses as much as digits as its factorization.

13581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 512 (or 506 counting only the distinct ones).

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

The square root of 13581 is about 116.5375475973. The cubic root of 13581 is about 23.8585428832.

Subtracting 13581 from its reverse (18531), we obtain a triangular number (4950 = T₉₉).

It can be divided in two parts, 135 and 81, that added together give a cube (216 = 6³).

The spelling of 13581 in words is "thirteen thousand, five hundred eighty-one".