(k^(n+1) *((-6*n^2+6*n+5) + (3*n^2-6*n-7) *k + (k^2-3*k+3)*(3*n^2-1)) + k^(2n+2) *(6*(n+1) + - 6*k*n) +k^(3*n+3) -2*k^2 -2*k) /(k-1)^3