Incomplete investigation suggests that Ei(x) = EulerMascheroniGamma + ln(x) + exp(R*x) * SUM(n>0) c[n] * x^n converges fastest (in the sense the |c[n]| shrink the fastest asymptotically) when R=1/2, Ramanujan's choice -- or if 1/2 is not optimum, it seems nearly optimum. How could that be proven? -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)