• 181 can be written using four 4's:
181 is nontrivially palindromic in base 10 and base 12.
It is the 6-th star number.
181 is an esthetic number in base 14, because in such base its adjacent digits differ by 1.
It is a weak prime.
It is a palprime.
It is a cyclic number.
It is a Chen prime.
It is an alternating number because its digits alternate between odd and even.
181 is a strobogrammatic number because it is the same when read upside-down.
181 is an undulating number in base 10 and base 12.
It is a plaindrome in base 7, base 11 and base 14.
It is a nialpdrome in base 9, base 15 and base 16.
It is a congruent number.
It is an amenable number.
181 is an equidigital number, since it uses as much as digits as its factorization.
181 is an odious number, because the sum of its binary digits is odd.
The square root of 181 is about 13.4536240471. The cubic root of 181 is about 5.6566528258.
Adding to 181 its sum of digits (10), we get a palindrome (191).
Subtracting from 181 its sum of digits (10), we obtain a palindrome (171).
The spelling of 181 in words is "one hundred eighty-one", and thus it is an aban number.