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I've been searching since a few days the symbol of Napier's number (e).

It is a symbol of and with a cut on the inside similary to the double struck commands (\mathbb). I vaguely remember that there is a package, perhaps distributed by Wolfram Alfa in a .zip file, which it can to be used in LaTeX documents. Currently I have not been able to find it.

Here there is a ugly screenshot (edit: slightly better screenshot from Wolfram|Alpha):

enter image description here

Related question: Truncation of Napier’s number (e) to an amount of decimal digits of my choice

Marijn
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Sebastiano
  • 54,118

1 Answers1

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It's ⅇ U+2147 (ⅇ in HTML) so should be available in in any font that has double struck italic lower case. So any font used with unicode-math or for pdftex for example the stix and stix2 packages will make it available.

Actually I don't see it in the stix2 package which is surprising, with unicode-math it is

enter image description here

\documentclass{article}

\usepackage{unicode-math}

\begin{document}

$ \mitBbbe^i $

\end{document}

That is latin modern but any OpenType math font will have this.

David Carlisle
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  • I always thank you for your kindness as Marijn that Have edited my question and he has finded a best image. Some time ago I found a series of .zip files that connected to LaTeX but I can't find it no more. – Sebastiano Jan 19 '20 at 21:25
  • I have seen (in fact) stix and stix2 package documentation and I have not finded it. – Sebastiano Jan 19 '20 at 21:32
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    @Sebastiano if you have mathematica you can use these https://ctan.org/pkg/mathematica?lang=en but I don't think the fonts are generally available any more. But as always you should not worry about the exact character shape, use the font that matches your document. No point in using the mathematica fonts for just one character. – David Carlisle Jan 19 '20 at 21:33
  • U+2147 should be in stix2; it's certainly in the copy of the reference table I kept when I left AMS, although the name in that table is still \itBbbe. \mitBbbe, as in unicode-fonts, is the agreed "correct" name. – barbara beeton Jan 19 '20 at 21:46
  • I think it should be also a double-struck i for the imaginary unit following the Wolfram conventions: $^$ or $ⅇ^ⅈ$. And a double-struck differential d: $∫^x \, x = ^x + c$ or $∫ⅇ^x \, ⅆx = ^x + c$ :) – Weißer Kater Jan 19 '20 at 21:47
  • @user125730 I wondered about using ⅈ but the whole convention is so horrible I couldn't bring myself to do it other than for the explicitly asked e :-) – David Carlisle Jan 19 '20 at 22:00
  • @barbarabeeton neither \itBbbe nor \mitBbbe is defined in stix or stix2 packages for pdftex. – David Carlisle Jan 19 '20 at 22:03
  • @DavidCarlisle Why do you think that this convention is horrible? There is an argument for it: If you use and , e and i will be free for other usages. For example, ∑_{i=1}^{n} ... does not disturb any more when you deal with complex numbers. ;) Or something like d/d = 1 is better than dd/dd = d²/d² = 1. OK, my last example is a little bit crazy. :D – Weißer Kater Jan 19 '20 at 22:30
  • @user125730 some things just look horrible. – David Carlisle Jan 19 '20 at 22:46