“…Moreover, s L (G) has been investigated for various other sets, including: [1, k] for k ≥ exp(G) (see, e.g., [4,2,6]), {k exp(G)} for k ∈ N (see, e.g., [13,26]), N \ kN for k ∤ exp(G) and other unions of arithmetic progressions (see [7,29,21]), and exp(G)N (see, e.g., [3]). And, for recent closely related results, see, e.g., [23,9,12,22,11,31].…”