171 (number)
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171 is a natural number between 170 and 172. It is an odd number, meaning it cannot be divided evenly by two. In base ten, it consists of three digits: 1, 7, and 1.
171 is a composite number, not a prime number. It has six divisors: 1, 3, 9, 19, 57, and 171. Its prime factorization is 3 × 3 × 19, also written as 3² × 19.
Mathematical properties
171 is a triangular number: it is the sum of the integers from 1 to 18, following the formula n(n+1)/2 when n = 18. Therefore 171 dots can be arranged in an equilateral triangle with 18 objects along its base.
The sum of the digits of 171 is 1 + 7 + 1 = 9. Since 9 is divisible by 9, the number itself is also divisible by 9 (171 ÷ 9 = 19). Because the number is divisible by the sum of its digits, 171 is a Harshad number in base ten.
Representations in other bases
In binary, 171 is written as 10101011. In Roman numerals it is CLXXI. The digit sum of 171 is not a palindrome when read backwards—reading it in reverse gives 171 itself, so it is in fact a palindromic number in base ten.