181981 has 2 divisors, whose sum is σ = 181982. Its totient is φ = 181980.

The previous prime is 181967. The next prime is 181997. The reversal of 181981 is 189181.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 164025 + 17956 = 405^2 + 134^2 .

It is a cyclic number.

It is not a de Polignac number, because 181981 - 2¹⁵ = 149213 is a prime.

It is a super-2 number, since 2×181981² = 66234168722, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (181931) 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 as a sum of consecutive naturals, namely, 90990 + 90991.

It is an arithmetic number, because the mean of its divisors is an integer number (90991).

2¹⁸¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

181981 is a deficient number, since it is larger than the sum of its proper divisors (1).

181981 is an equidigital number, since it uses as much as digits as its factorization.

181981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 576, while the sum is 28.

The square root of 181981 is about 426.5923112294. The cubic root of 181981 is about 56.6685389616.

The spelling of 181981 in words is "one hundred eighty-one thousand, nine hundred eighty-one".