biserial ratio of correlation

The definition of double equal ratio series is given in the paper and the general term and formula of former n terms are given.

给出了双等比数列的定义和三等比数列概念,推证出双等比数列和三等比数列的通项公式和前n项和公式,最后给出了三等比数列的概念、通项公式和前n项和公式。