Adding Consecutive Terms of Arbitrary Fibonacci Sequence, Method 2

This alternative method for summing the first $n$ terms of an Arbitrary Fibonacci Sequence ($A_n$) uses the Standard Fibonacci numbers ($F_n$). This method is calculation-intensive but does not require you to find later terms in the arbitrary sequence.

Sum = $A_1 \times F_n + A_2 \times (F_{n+1} - 1)$

For the sequence 4, 7, 11, ... ($A_1=4, A_2=7$), the sum of the first 7 terms is: $4 \times F_7 + 7 \times (F_8 - 1) = 4 \times 13 + 7 \times (21 - 1) = 52 + 140 = 192$. This requires memorization of the standard Fibonacci numbers.