2nCn−1{ }^{2 n} C_{n-1}2nCn−1
nCn{ }^{n} \mathrm{C}_{n}nCn
2nCn+1{ }^{2 n} C_{n+1}2nCn+1
2nCn+2{ }^{2 n} C_{n+2}2nCn+2