Adding Odd or Even Terms of Arbitrary Fibonacci Sequence

There are specific formulas for summing only the odd-indexed or even-indexed terms of an Arbitrary Fibonacci Sequence.

Sum of the first n odd terms ($A_1, A_3, ...$):

$\sum_{i=1}^{n} A_{2i-1} = A_{2n} - (A_2 - A_1)$

Sum of the first n even terms ($A_2, A_4, ...$):

$\sum_{i=1}^{n} A_{2i} = A_{2n+1} - A_1$

These formulas require you to know a future term in the sequence, which you may need to calculate or have memorized if it's the standard sequence.