170 (Number)
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170 is a natural number that comes after 169 and before 171. It is an even and composite number, meaning it has divisors other than 1 and itself. In Roman numerals it is written as CLXX.
The prime factorization of 170 is 2 × 5 × 17. For this reason, 170 is a sphenic number, defined as the product of exactly three distinct prime factors.
Divisors
The divisors of 170 are 1, 2, 5, 10, 17, 34, 85, and 170. The sum of all divisors (σ) is 324. The sum of proper divisors (those less than 170) is 154, which is less than 170; therefore 170 is a deficient number.
Mathematical properties
Euler's totient function (φ), which counts numbers less than 170 that share no common factor with it, gives φ(170) = 64. Both 64 and 324 are perfect squares (8² and 18²). 170 is noted as the smallest number for which both φ(n) and σ(n) are perfect squares.
170 can be expressed as the sum of two perfect squares in two ways: 170 = 1² + 13² and 170 = 7² + 11². It also follows from 169 = 13², so 170 = 13² + 1.
Other number systems
In binary (base-2), 170 is 10101010, an alternating pattern of 1s and 0s. In hexadecimal (base-16) it is AA. For this reason, 170 is often used as an example in computer mathematics, particularly when explaining bit patterns.