\operatorname{erf} (x) = \frac{2}{\sqrt{\pi}} x - \frac{2}{3 \sqrt{\pi}} x^{3} + \frac{1}{5 \sqrt{\pi}} x^{5} - \frac{1}{21 \sqrt{\pi}} x^{7} + \frac{1}{108 \sqrt{\pi}} x^{9} - \\ \quad{}\quad{}\frac{1}{660 \sqrt{\pi}} x^{11} + \frac{1}{4680 \sqrt{\pi}} x^{13} - \frac{1}{37800 \sqrt{\pi}} x^{15} + \operatorname{O} \bigl(x^{16}\bigr)

`&operatorname`(erf)(x) = series(2/Pi^(1/2)*x+(-2/3/Pi^(1/2))*x^3+1/5/Pi^(1/2)*x^5+(-1/21/Pi^(1/2))*x^7+1/108/Pi^(1/2)*x^9+(-1/660/Pi^(1/2))*x^11+1/4680/Pi^(1/2)*x^13+(-1/37800/Pi^(1/2))*x^15+O(x^16),x,16)