more Π obscurantism

Here's an illustration of an approach to Π pointed out by Kevin Brown. Define f(n) as the nearest greater or equal multiple of n-1, then of n-2, etc (yielding OEIS sequence 2491). Then, inverting a result found by Duane Broline and Daniel Loeb, Π = n² / f(n).

But as you can see from the comment, the series converges very slowly!