If a is the first term then the series runs a+a/4+a/16+a/64+.. until the fraction becomes infinitesimally small. But let's not take it that far. We'll go as far as n. Let S=sum of the series up to n, so the last term in the series is a/4^n. Now consider multiplying the whole series by 1/4, so we get S/4=a/4+a/16+a/64+a/256+...+a/4^(n+1). Now subtract this new series from S and we get 3S/4=a-a/4^(n+1). As n approaches infinity a/4^(n+1) approaches zero, so we can drop the term and 3S/4=a. We know the converging value of the series S=20/3, therefore a=(3/4)*(20/3)=5. The first term is 5, the next term is 5/4, and so on.