I am trying to get the digit one printed the \mathbb{} font in math mode, however the command


outputs some rubbish. I certainly saw the character I am after in some pdf's generated from latex, hence my question: how do you get it to work?

  • 3
    possible duplicate of How do I make a blackboard 1? – Gonzalo Medina Aug 27 '11 at 15:04
  • The \mathbb provided as part of the amsfonts package does not provide numerals. Section 3.3 of amsfonts' documentation states that the \mathbb command it provides uses the msbm font and so supports only uppercase letters: no lowercase, no numerals. – mas Aug 27 '11 at 15:52
  • note that using any package that provides a complete blackboard bold font overrides the \mathbb provided by amsfonts. if you wish to replace only the digit "1", you can use the method described here: Importing a single symbol from a different font – barbara beeton Feb 13 '17 at 17:30
  • off topic: After years reading math texts, I think that the most common notation for the characteristic function of a set $A$ is \chi_A. – Sigur Feb 27 '18 at 11:25

Since \mathbb doesn't support digits (with amssymb or txfonts) you may use bbm

\[ \mathbbm{1} \]

bbm example

or dsfont, the doublestroke package:

\[ \mathds{1} \]

dsfont example

  • 5
    I guess \mathbbm{1}is the best in terms of consistency with \mathbb. – Alfredo Hernández Nov 28 '14 at 23:15
  • You can also add \newcommand{\1}[1]{\mathds{1}\left[#1\right]} to your preamble to create a quick indicator function that handles what you wanna put inside it. – Guilherme Salomé Nov 8 '16 at 23:07

Another option is to use bbold package.

\[ \mathbb{1} \]

bbold example

Though it ruins the letters.


I'm surprised no one has mentioned this, but you can use the unicode-math package. Note that you need Xe(La)TeX or LuaLaTeX to use this package.




enter image description here

% For documents in 10pt, 11pt or 12pt     
% \def\one{\mbox{1\hspace{-3.85pt}\fontsize{11}{14.4}\selectfont\textrm{1}}} % 10pt    
\def\one{\mbox{1\hspace{-4.25pt}\fontsize{12}{14.4}\selectfont\textrm{1}}} % 11pt    
% \def\one{\mbox{1\hspace{-4.75pt}\fontsize{13}{14.4}\selectfont\textrm{1}}} % 12pt    
You can use either $\one$ or $\one\{A\}$ or $\one_{A}$.

enter image description here

  • Welcome to TeX.SE. Do note that \rm is considered deprecated for a LaTeX document. It also doesn't take an argument; instead, it acts as a switch. Thus, instead of \rm{\fontsize{11}{14.4}\selectfont 1}, do write \fontsize{11}{14.4}\selectfont\textrm{1}. Also, is there something that can be done to produce less of an overlap/clash between the tops of the two 1 numeral? – Mico Feb 12 '17 at 16:27
  • The correct metrics depend on the font and font family, I guess. I typeset most of my documents with \usepackage{mathptmx}, a Times like font, and the code given works just perfectly. Adjust the argument of \hspace accordingly. – Jotazuma Feb 12 '17 at 17:19

This worked for me:



Actually, I'm using LyX, so I put \usepackage in the preamble and then simply used \mathbb with a 1 inside a formula box. It still displays as `rubbish' but renders fine as PDF.

If you don't like the discordance in LyX, you can say something like


in the preamble, and then use \bbone in your document, or variants on this theme.

My 2c.

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