*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, pi = n

^{2}/ f(n).

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

main = print $ e**2 / f e e 1 where e = 900000 -- yields 3.1416003... f n 1 _ = n f n k l = f n' (k - 1) $ n' / k where n' = head $ dropWhile (< n) $ map (* k) [l..]

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