Xin hay nhất nhé tus^^
$S_{1}$ = 1 + 2 + $2^{2}$ + $2^{3}$ +...+ $2^{63}$
2$S_{1}$ = 2 + $2^{2}$ + $2^{3}$ + $2^{4}$ +...+ $2^{64}$
2$S_{1}$ - $S_{1}$ = (2 + $2^{2}$ + $2^{3}$ + $2^{4}$ +...+ $2^{64}$) - (1 + 2 + $2^{2}$ + $2^{3}$ +...+ $2^{63}$)
$S_{1}$ = $2^{64}$ - 1