171

171 is the natural number that follows 170 and precedes 172. It is an odd composite number whose prime factorization is 3^2 × 19.

Its divisors are 1, 3, 9, 19, 57, and 171. The sum of its proper divisors is 89, which is less than 171, so 171 is a deficient number. The sum of its digits is 9, and since 9 divides 171, it is a Harshad (Niven) number in base 10. 171 is also the 18th triangular number, as 18 × 19 / 2 equals 171.

In terms of numeral representations, 171 is 10101011 in binary, AB in hexadecimal, and 253 in octal. In Roman numerals it is written as CLXXI.

In broader context, 171 is not a prime, nor a perfect square or cube, and it commonly appears in discussions of triangular numbers and digit-sum divisibility properties. It is used in calendar notation for years such as 171 CE/AD, where historical events would depend on the region and source consulted. As a number, 171 serves as an example of a small, composite integer with a simple factorization and several standard representations across numeral systems.