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I'm stuck on this problem:

$$1 + {1\cdot2\over1\cdot3} + {1\cdot2\cdot3\over1\cdot3\cdot5}+ {1\cdot2\cdot3\cdot4\over 1\cdot3\cdot5\cdot7} +\cdots$$

I've simplified the numerators $n!$ but can't figure out how to represent the denominators.

How do I go about solving this?

3 Answers 3