Is it possible to include $math$ inside flextables?

I would like to have some fancy equations within a nicely formatted table. Is it possible to use flextable to achieve this?

library(flextable)
df <- data.frame(FancyMath= c("$A^{-1}$", "$A = pi~r^2$"))
flextable(df)

The $ $ notation is not creating Math-style writing as I would expect. Thanks!