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Non - Zero Digit II (Posted on 2012-02-05) Difficulty: 4 of 5
Reading from left to right, what is the last non - zero digit in ((20!)!)!? (That is, the factorial of factorial of 20 factorial).

No Solution Yet Submitted by K Sengupta    
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re: No Subject Comment 7 of 7 |
(In reply to No Subject by Benny)

I hadn't looked at all of the links on the oeis entry.  That is the most straightforward algorithm I've seen.

If only there were an easy way to put (20!)! into base 5.

What we need is some type of formula that lets us reduce a((n!)!) to something smaller.

For example if there were a way of figuring out a(n) from a(n!) we'd be all set.

  Posted by Jer on 2012-02-07 12:29:20

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