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I saw this symbol: $\underline{\big|6} $ in a question bank for a chapter of permutations and combinations. I have included the question from the book to provide more context: image link.

Mason
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Rajdeep Biswas
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    Unless it's just a typo, I have no idea. – lulu Dec 14 '18 at 19:20
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    The symbol means $6!$ – Shubham Johri Dec 14 '18 at 19:21
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    That's an old symbol for the factorial of a number. It was mostly phased out by the early 1900s, but you can find it in most 1800s algebra textbooks. – Dave L. Renfro Dec 14 '18 at 19:21
  • Use of this symbol is referenced in this answer and the comments indicate a usage by Hilbert. – Mason Dec 14 '18 at 19:26
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    @DaveL.Renfro Make an answer out of your comment :) – mrtaurho Dec 14 '18 at 19:28
  • @mrtaurho: (and Rajdeep Biswas) I decided to expand my answer by giving some excerpts from Cajori's paper, partly because the paper is behind a paywall and thus many people will not have access to it (indeed, I don't have digital access to it) and partly because it seems that much of what I've found from internet searches is very sparse and repetitive. However, because this question is marked as a duplicate of a question that seems to be a better place for these excerpts, I've posted the excerpts here. – Dave L. Renfro Dec 15 '18 at 09:04

1 Answers1

6

This an old symbol for the factorial of a number. It was mostly phased out by the early 1900s, but you can find it in most 1800s literature, especially mathematicians in Great Britain. A useful historical survey of various notations for factorial is given in

Florian Cajori, History of symbols for $\underline{n}=$ factorial, Isis 3 #3 (Summer 1921), 414-418.

Dave L. Renfro
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