← Complete problem index

PROJECT EULER · #0140

Modified Fibonacci Golden Nuggets

Statement only · SolvedOriginal problem ↗

Consider the infinite polynomial series AG(x)=xG1+x2G2+x3G3+, where Gk is the kth term of the second order recurrence relation Gk=Gk1+Gk2, G1=1 and G2=4; that is, 1,4,5,9,14,23,.

For this problem we shall be concerned with values of x for which AG(x) is a positive integer.

The corresponding values of x for the first five natural numbers are shown below.

xAG(x)
5141
252
22263
1375144
125

We shall call AG(x) a golden nugget if x is rational, because they become increasingly rarer; for example, the 20th golden nugget is 211345365.

Find the sum of the first thirty golden nuggets.

Write-up coming later

The complete problem is available here. An approach, code, and answer will be added later.