How to create a formula with iterations / sequences

I would like to adapt in Pigment a simple formula used in excel (Metric 1 in yellow, with details in cell F2) :

NB : The grey cell C2 is a manual input initiating the sequence.

Issue: as the calculation is like a sequence using each previous value, there would be iterations within the same metric.

I’ve tried the below formula to overcome the issue, it works for few months but you can see it’s not scalable: