155781 has 12 divisors (see below), whose sum is σ = 237120. Its totient is φ = 98280.

The previous prime is 155777. The next prime is 155783. The reversal of 155781 is 187551.

It is not a de Polignac number, because 155781 - 2² = 155777 is a prime.

It is a super-2 number, since 2×155781² = 48535439922, which contains 22 as substring.

It is a Smith number, since the sum of its digits (27) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155783) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 285 + ... + 626.

It is an arithmetic number, because the mean of its divisors is an integer number (19760).

2¹⁵⁵⁷⁸¹ is an apocalyptic number.

It is an amenable number.

155781 is a deficient number, since it is larger than the sum of its proper divisors (81339).

155781 is a wasteful number, since it uses less digits than its factorization.

155781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 936 (or 933 counting only the distinct ones).

The product of its digits is 1400, while the sum is 27.

The square root of 155781 is about 394.6910183929. The cubic root of 155781 is about 53.8069236493.

The spelling of 155781 in words is "one hundred fifty-five thousand, seven hundred eighty-one".