I'd like to just have a few inline formulas evaluated in my org-mode
document (I'm exporting to LaTeX if that matters). Something like this:

=========================
# a constant:
# pi = 3.14159

The value of interest is {{{2*$pi}}}.
=========================

I want that to export as:

  The value of interest is 6.28318.

Of course I made up that {{{}}} syntax, that's not a real thing. I've seen
org-mode tables with calc, but I'm hoping for something simpler, just
inline math expression eval. (I'm fine with elisp, calc, whatever.)

Possible?

-- 
Gary