Problem 84. Longest Divisor Run

Given the vector a, find the longest run of consecutive numbers that can be evenly divided by the same number d where d > 1.

Example:

 Input  a = [5 4 2 8 3 7 14]
 Output len is 3, d is 2 

The last two numbers, 7 and 14, are divisible by 7, but the run of numbers [4 2 8] are all divisible by 2. So the longest run is 3. You can assume that d is unique.