7. Express the polynomial in $x$
$$
f(x)=1-x+x^{2}-x^{3}+\cdots-x^{19}+x^{20}
$$

as a polynomial in $y$
$$
g(y)=a_{0}+a_{1} y+\cdots+a_{20} y^{20},
$$

where $y=x-4$. Then $a_{0}+a_{1}+\cdots+a_{20}=$
$\qquad$