Question 172
Express the polynomial in $x$ $f(x) = 1 - x + x^2 - x^3 + \cdots - x^{19} + x^{20}$ into a polynomial in $y$ $g(y) = a_0 + a_1 y + a_2 y^2 + \cdots + a_{19} y^{19} + a_{20} y^{20}$, where $y = x - 4$. Then $a_0 + a_1 + \cdots + a_{20} = \text{\_\_\_\_\_\_\_\_\_}$.