a | b conditional ๐ ๐ {\displaystyle{\displaystyle a|b}} a โฃ b conditional ๐ ๐ {\displaystyle{\displaystyle a\mid b}} 2 โข n !! 2 double-factorial ๐ {\displaystyle{\displaystyle 2n!!}} โ n = 0 โ 1 n superscript subscript ๐ 0 1 ๐ {\displaystyle{\displaystyle\sum_{n=0}^{\infty}\frac{1}{n}}}