f(k;n,p)=nCkpk(1−p)n−k=n!k!(n−k)!pk(1−p)n−k=Γ(n+1)Γ(k+1)Γ(n−k+1)pk(1−p)n−k=pk(1−p)n−kB(k+1,n−k+1)(n+1)