There's a wishing well, the first wish costs 6 golden coins, the second costs 12, the third costs 24 and so on.

Question

There's a wishing well, the first wish costs 6 golden coins, the second costs 12, the third costs 24 and so on. The total of making three wishes is the sum of the gold spent to make all the wishes, so: 6+12+24=42 golden coins. How much would it costs to make 200 wishes? I need a formula to calculate it.

Answer 1

S_n = a₁(1 - rⁿ) / (1 - r)

S₂₀₀ = 6(1 - 2²⁰⁰) / (1 - 2)

 

Can you calculate and answer?