Ever wondered how to type that fancy double-struck number “1” in your math equations? You know, the one that pops up when you’re trying to write the indicator function? Don’t worry—it’s more common than you might think, and typing it can be super fun once you know how!
Let’s break it down in a simple and friendly way. Whether you’re writing in LaTeX, using Microsoft Word’s equation editor, or programming in Python, there’s a way to type it just right!
What Is the Double-Struck 1?
The double-struck 1, written as 𝟙, is a special mathematical symbol. It’s used to represent the indicator function. This function is all about determining whether something is part of a set.
If the element is in the set, the function returns 1. If not? It returns 0. That’s why the 𝟙 is used—it visually reminds us it’s checking for membership!
So how do we type this magical-looking 𝟙? Let’s look at a few ways.
Option 1: Using LaTeX
LaTeX is a gift to math lovers 
To get the double-struck 1 in LaTeX, try this:
\mathbb{1}
This command tells LaTeX to use the blackboard bold style, which is how you get that double-struck vibe.
It’ll show up in your document like this: 𝟙
But wait! Sometimes, the \mathbb{} command only works with capital letters in some setups. If you run into trouble with \mathbb{1}, don’t panic. Just use a LaTeX package like amssymb or dsfont for better results.
Here’s a tip:
Add this to your preamble to make sure it works:
\usepackage{dsfont}
Then type:
\mathds{1}
BOOM 
You’ve got your indicator function ready to go!
Option 2: In Microsoft Word (Equation Editor)
If you’re using Microsoft Word’s equation editor, it might not let you directly type a blackboard bold 𝟙. But don’t give up!
Here’s what you can try:
- Type an equation using Alt + = to open the equation box.
- Type
\mathbb{1}and see if it works. - If it doesn’t, go for a Unicode shortcut, or paste it directly into your document from a site like unicode-table.com.
The Unicode for double-struck 1 is U+1D7D9. Pretty cool, huh?
You can also copy and paste it straight from here: 𝟙
Option 3: In Programming
If you’re a coder, you may want ways to type or represent 𝟙 too. In Python, for example, you may not need the fancy symbol for calculations—just use a normal 1.
But if you’re generating pretty math output in Jupyter or using matplotlib, you can use LaTeX inside strings:
plt.title(r"$\mathbb{1}_{A}(x)$")
This shows a 𝟙 with a subscript A, like for an indicator function over a set A.
Use “r” before the string to make sure Python reads it correctly!
One More Trick: Copy-Paste Superpowers 
If all else fails, just copy it: 𝟙. Boom. You’re done. Paste it wherever you need!
Want even more math font magic? Google “double-struck unicode characters”—there’s a whole family of fancy numbers and letters!
Summary: Your 𝟙 Toolbox
- LaTeX: Use
\mathbb{1}or\mathds{1} - Microsoft Word: Try
\mathbb{1}in equation editor or paste Unicode - Python/matplotlib: Use LaTeX strings in your plots
- Fastest of all: Just copy 𝟙 and go!
The double-struck 1 is like a superhero in disguise. Small, but mighty. Next time you need an indicator function, you’ll know just what to do!