Not only is mdillon's solution correct, it's also much more efficient as each factorial is simply one multiply on the previous one, whereas calling the function each time means a lot more work is being done.

Now the reason for the failure is that the Math::NumberCruncher function overflows for 171!. Unfortunately it returns '1.#INF' which Perl happily treats as 1.0 in your division, so you simply divide by one from that point on, not making much more progress.

Update: While Math::NumberCruncher does not use BigFloats for it's factorial function, it does already use the Math::BigFloat module for storing its very large version of $PI (though strangely BigFloats are not used in calculations with that $PI so it's probably pointless...), so it is a trivial matter to patch Math::NumberCruncher to use a BigFloat for the factorial. This is of course for occasional uses as for an iterative use of factorial mdillon's answer is still much faster.

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I'd like to be able to assign to an luser

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