Sorry bout the dumb question, it's just that I'm taking a mathematical finances class and the teacher started using this symbol today but I've never seem it before, was trying to google it but don't know its name and searching for the symbol itself yields 0 results.!
It's the $┐$ in the following equation.
$$A = R \frac{1 − (1 + i)^{− n}}{i} (1 + i) = R \,a_{\overline{n}|i}\, (1 + i)$$
There are also these other equations here
$a_{\overline{n}|i}$ (read a-angle-n at i) is the present value of an annuity-immediate: $$ a_{\overline{n}|i}=\frac{1-(1+i)^{-n}}{i}=\frac{1-v^n}{i}\qquad\text{with}\;v=\frac{1}{1+i} $$