Sentence:  While applying his willful kind of calculus to Newton's <WSD>binomial series</WSD>, Euler not only constructed the exponential function, but found out that its inverse had already been in the minds of the 17th century and thus detected the very nature of logarithms. 
Meaning of the word marked with <WSD> tags:  The Maclaurin series expansion of the function "f"("x")  = (1 + "x")"α", for arbitrary complex "α"; the series \textstyle\sum_{k=0}^\infty{\alpha \choose k} x^k, where \textstyle{\alpha \choose k} = \frac{\alpha(\alpha-1)(\alpha-2)·s(\alpha-k+1)}{k!}.