How do I figure out progressive savings on excel?

I've figured it out before, but I lost the Excel formula. You deposit $1 the first day, the next day you deposit $1, and each next day, you increase your deposit by $1. This works for any currency. Does anyone know what the excel formula for this might be? If I recall correctly, at deposit 100 which would be a $100 deposit, if you still have the previous deposits, you will have $5050. But I want the excel worksheet for this. Theoretically it'll put you into the millions. Theoretically. Since you won't likely be able to afford to keep it up for a long time, I'd suggest resetting back to $1 when you top out. Each time you must reset, you will lively reset at a higher number. But I need that formula.

And I hope I've opened eyes to a great idea too.