155581 has 2 divisors, whose sum is σ = 155582. Its totient is φ = 155580.

The previous prime is 155579. The next prime is 155593. The reversal of 155581 is 185551.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 152100 + 3481 = 390^2 + 59^2 .

It is an emirp because it is prime and its reverse (185551) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 155581 - 2¹ = 155579 is a prime.

It is a super-2 number, since 2×155581² = 48410895122, which contains 22 as substring.

Together with 155579, it forms a pair of twin primes.

155581 is a lucky number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (155501) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77790 + 77791.

It is an arithmetic number, because the mean of its divisors is an integer number (77791).

2¹⁵⁵⁵⁸¹ is an apocalyptic number.

It is an amenable number.

155581 is a deficient number, since it is larger than the sum of its proper divisors (1).

155581 is an equidigital number, since it uses as much as digits as its factorization.

155581 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1000, while the sum is 25.

The square root of 155581 is about 394.4375742751. The cubic root of 155581 is about 53.7838870502.

The spelling of 155581 in words is "one hundred fifty-five thousand, five hundred eighty-one".