Ok so look for the change between x and y.
Try to divide by each prime number starting with 2. If it is divisible, keep trying the same prime number until it is not divisible. Then move on to the next prime number, 3. Keep dividing until you get 1. All the prime numbers you divided by are the prime factorization.
List of the first several prime numbers: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29
Start with 85.
85 is not divisible by 2.
Move on to 3.
85 is not divisible by 3.
Move on to 5.
85/5 = 17
17 is a prime number, so now divide 17 by 17.
17/17 = 1
We divided just by 5 and 17.
Answer: The prime factors of 85 are 5 and 17.
![\displaystyle\lim_{n\to\infty}\sqrt[n]{\left|\left(\frac{5n+15}{2n-1}\right)^n\right|}=\lim_{n\to\infty}\frac{5n+15}{2n-1}=\dfrac52](https://tex.z-dn.net/?f=%5Cdisplaystyle%5Clim_%7Bn%5Cto%5Cinfty%7D%5Csqrt%5Bn%5D%7B%5Cleft%7C%5Cleft%28%5Cfrac%7B5n%2B15%7D%7B2n-1%7D%5Cright%29%5En%5Cright%7C%7D%3D%5Clim_%7Bn%5Cto%5Cinfty%7D%5Cfrac%7B5n%2B15%7D%7B2n-1%7D%3D%5Cdfrac52)
Since this limit exceeds 1, the series diverges.
