ϕ ϕ^{1}(n) = ϕ(n) ϕ^{k}(n) = ϕ(ϕ^{k−1}(n)) k ≥ 2 S(n) = ϕ(n) + ϕ^{2}(n) + ⋯ + ϕ^{c}(n) + 1 ϕ^{c}(n) = 2