5581 has 2 divisors, whose sum is σ = 5582. Its totient is φ = 5580.

The previous prime is 5573. The next prime is 5591. The reversal of 5581 is 1855.

It is the 31-st star number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 4356 + 1225 = 66^2 + 35^2 .

It is a cyclic number.

It is not a de Polignac number, because 5581 - 2³ = 5573 is a prime.

It is a super-2 number, since 2×5581² = 62295122, which contains 22 as substring.

It is a Chen prime.

It is a plaindrome in base 16.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (5501) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2790 + 2791.

It is an arithmetic number, because the mean of its divisors is an integer number (2791).

2⁵⁵⁸¹ is an apocalyptic number.

It is an amenable number.

5581 is a deficient number, since it is larger than the sum of its proper divisors (1).

5581 is an equidigital number, since it uses as much as digits as its factorization.

5581 is an evil number, because the sum of its binary digits is even.

The product of its digits is 200, while the sum is 19.

The square root of 5581 is about 74.7060907825. The cubic root of 5581 is about 17.7379737355.

It can be divided in two parts, 55 and 81, that added together give a triangular number (136 = T₁₆).

The spelling of 5581 in words is "five thousand, five hundred eighty-one".