User blog comment:Swooped me in one hit/MCSICKLE/@comment-29310326-20170213182322/@comment-30754445-20170213190646

Nice.

It's exactly like the construction of Graham's number, only with 2 at the top (instead of 4) and 2 layers instead of 64.

As for an approximation... Well, 5↑↑5 = 5↑5↑5↑5↑5 = 5↑5↑5↑3125 ~ 5↑5↑(10↑2184) = 10↑10↑10↑2184.

So your number is about 10↑↑↑↑↑...↑↑↑↑↑10 (with 10↑10↑10↑2184 arrows). This is a sound approximation, because it doesn't matter whether we you 5's or 10's here. The only thing that matters is the number arrows.

And in letter notation this can be written as JEEE2184, or as K2-1-4-3-2184 (or if you prefer a real number at the end: K2.219)