For a fixed integer D(≥3)\documentclass[12pt]{minimal}
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\begin{document}$$D (\ge 3)$$\end{document} and λ\documentclass[12pt]{minimal}
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\begin{document}$$\lambda $$\end{document}∈\documentclass[12pt]{minimal}
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\begin{document}$$\in $$\end{document}Z+\documentclass[12pt]{minimal}
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\begin{document}$${\mathbb {Z}}^+$$\end{document}, a λ\documentclass[12pt]{minimal}
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\begin{document}$$\lambda $$\end{document}-L(D, 2, 1)-labeling of a graph G=(V,E)\documentclass[12pt]{minimal}
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\begin{document}$$G = (V, E)$$\end{document} is the problem of assigning non-negative integers (known as labels) from the set {0,…,λ}\documentclass[12pt]{minimal}
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\begin{document}$$\{0, \ldots , \lambda \}$$\end{document} to the vertices of G such that if any two vertices in V are one, two and three distance apart from each other, then the assigned labels to these vertices must have a difference of at least D, 2 and 1, respectively. The vertices which are at least 4 distance apart can receive the same label. The minimum value among all the possible values of λ\documentclass[12pt]{minimal}
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\begin{document}$$\lambda $$\end{document} for which there exists a λ\documentclass[12pt]{minimal}
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\begin{document}$$\lambda $$\end{document}-L(D, 2, 1)-labeling is known as the labeling number. In this paper, λ\documentclass[12pt]{minimal}
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\begin{document}$$\lambda $$\end{document}-L(D, 2, 1)-labeling of square grid is considered. The lower bound on the labeling number for square grid is presented, and a formula for λ\documentclass[12pt]{minimal}
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\begin{document}$$\lambda $$\end{document}-L(D, 2, 1)-labeling of square grid is proposed. The correctness proof of the proposed formula is given here. The upper bound of the labeling number obtained from the proposed labeling formula for square grid matches exactly with the lower bound of the labeling number.
