series%20for%201/((1-a%20x%5E(215/100))(1-b%20x%5E(275/100))(1-c%20x%5E(335/100))(1-d%20x%5E(355/100))(1-e%20x%5E(420/100))(1-f%20x%5E(580/100)))%20at%20x=0

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