After the first term, each term in a sequence is five times greater

I understand why you'd ask, because with percents, that's how things work, but things work differently with numbers. This won't seem logical (and it isn't, really), but when we say one number is five times greater than another, that just means the first number is five times the second number. With percents, on the other hand, if we say one number is 500% greater than another, that means the first number is six times the second. That might seem completely inconsistent, but language is just based on conventions, and that's how these phrases are used in practice (it's also why no one ever says "x is one times greater than y" to mean "x is twice as big as y").

That said, I don't think I've ever seen a real GMAT question use this kind of wording -- it can always be easily avoided, and I only ever it in prep company questions. For GMAT purposes, the important thing to understand is what the phrase "x is 500% greater than y" means (x = 6y), and not what the phrase "x is 5 times greater than y" means (x = 5y).