The combination formula of $C(n,k_1,k_2)$ is defined as:

$C(n,k_1,k_2)=(\frac{n}{k_1})(\frac{n-k_1}{k_2}).$

And the $C(n,k)$ formula is defined as:

$C(n,k_1,k_2)C(n,k)C(n,k_1,k_2)n,k_1{k}_{2}C(n,k_1,k_2)k_1{k}_2$