Fibonacci golden nuggets
Problem 137
Consider the infinite polynomial series , where is the th term in the Fibonacci sequence: ; that is, , and .
For this problem we shall be interested in values of for which is a positive integer.
The corresponding values of x for the first five natural numbers are shown below.
| 1 | |
| 2 | |
| 3 | |
| 4 | |
| 5 |
We shall call a golden nugget if is rational, because they become increasingly rarer; for example, the 10th golden nugget is 74049690.
Find the 15th golden nugget.