Equation 97 in http://mathworld.wolfram.com/PiFormulas.html introduces this notation I have never seen before:
$\left(\displaystyle\frac12\right)^3_n$
Everyone knows that 3 is an exponent, but what the heck is the $n$ doing down there???
I've tried googling this but I have no clue what to google. The source of these formulas cost $$$.