It is called symbol.equation.gpt
It is hosted in CRAN: https://cran.r-project.org/web/packages/symbol.equation.gpt/index.html
It is a really easy to use user interface, with just few clicks to prepare your equation and convert to Rmarkdown. Really cool.
install.packages("symbol.equation.gpt")
library("symbol.equation.gpt")
# Start user interface by going to ADDINS in RSTUDIO -> find symbols and equations