Yet another π formula

[ttw]

One problem for all methods is that the last few iterations may dominate in that these must be done to really large precision. Some years ago (about the time of the first trillion digits computation) it was noted that the last division of sizes around 1,000,000, leading to the 1,000,000,000,000 digits takes most of the time in the computation. It completely dominated (at that time) the computation of the previous terms.

Fast (fourth order) methods were not much faster than first order or second order computations.

The online stuff nice (but it's base 16) and requires a trillion digit base conversion at the end.