181666 has 4 divisors (see below), whose sum is σ = 272502. Its totient is φ = 90832.

The previous prime is 181639. The next prime is 181667. The reversal of 181666 is 666181.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 143641 + 38025 = 379^2 + 195^2 .

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (181667) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 45415 + ... + 45418.

2¹⁸¹⁶⁶⁶ is an apocalyptic number.

181666 is a deficient number, since it is larger than the sum of its proper divisors (90836).

181666 is an equidigital number, since it uses as much as digits as its factorization.

181666 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 90835.

The product of its digits is 1728, while the sum is 28.

The square root of 181666 is about 426.2229463555. Note that the first 3 decimals coincide. The cubic root of 181666 is about 56.6358232767.

The spelling of 181666 in words is "one hundred eighty-one thousand, six hundred sixty-six".