Alan's Quiz Question - For a tenner

After my success answering Annec's question, its my turn. However, I’m not clever enough for an ‘Italian’ question – so I’ll go for one with a ‘Greek’ connection insteadI’m a ‘sad’ man who likes numbers. I discovered a series of numbers that I use as a mental exercise - in working things out, and keeping my brain active. When I say 'discovered', I'm sure it has been found out before, but I found it again from scratchThe first two groups in the sequence [where the first number is always odd] are:-3, 5, 45, 13, 12For a tenner to the Earthquake Fund– 1, what is the 4th group?and2. What can the sequence be used for