You could shorten it to: {title}{series:| (|, }{series_index:|Book |)}
The 0>1s part says format with leading zeros, to have a minimum width of 1, of type string. You got this from the calibre manual for the template language? If so, they used this here (with a 3 not a 1) to make sure series displays as 001, 002, 003, ... , 009, 010, 011, etc.
The template language is a bit hard to understand, but this is what's happening. And you could just let it default to always displaying everything, by just not including that chunk. Or leave it alone because it still works, albeit in a visually confusing manner.
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