ta có 2^{2n+1}= C^{0}_{2n+1} + C^{1}_{2n+1}+......+C^{n}_{2n+1}+.....+C^{2n}_{2n+1} +c^{2n+1}_{2n+1}C^{0}_{2n+1} = C^{2n+1}_{2n+1}...C^{n}_{2n+1} = c^{n+1}_{2n+1}\Rightarrow 2^{2n+1} = 2(C^{0}_{2n+1} +....+C^{n}_{2n+1})\Rightarrow (C^{0}_{2n+1} +....+C^{n}_{2n+1}) = 2^{2n}\Rightarrow C^{1}_{2n+1}+....C^{n}_{2n+1} = 2^{2n} -1=2^{20} -1\Rightarrow n=10
ta có
$2^{2n+1}= C^{0}_{2n+1} + C^{1}_{2n+1}+......+C^{n}_{2n+1}+.....+C^{2n}_{2n+1} +c^{2n+1}_{2n+1}
$$C^{0}_{2n+1} = C^{2n+1}_{2n+1}
$...
$C^{n}_{2n+1} = c^{n+1}_{2n+1}
$$\Rightarrow 2^{2n+1} = 2(C^{0}_{2n+1} +....+C^{n}_{2n+1})
$$\Rightarrow (C^{0}_{2n+1} +....+C^{n}_{2n+1}) = 2^{2n}
$$\Rightarrow C^{1}_{2n+1}+....C^{n}_{2n+1} = 2^{2n} -1=2^{20} -1
$$\Rightarrow n=10
$