[1] A. Cayley, Theory of groups, graphical representation, Mathematical Papers, Cambridge 10 (1895) 26-28.
[2] P. Zhang and G. Chartrand, Introduction to Graph Theory, Tata McGraw-Hell Edition, 2006.
[3] Z. Chen, Harary’s conjectures on integral sum graphs, Discrete Math., 160 (1996) 241-244.
[4] J. A. Gallian, A dynamic survey of graph labeling, Electron. J. Combin., 1 No. DynamicSurveys (2018) DS6.
[5] N. Hartsfield and G. Ringel, Pearls in Graph Theory, Academic Press, United Kingdom, 1994.
[6] F. Harary, Sum graph over all the integers, Discrete Math., 124 No. 1-3 (1994) 99-105.
[7] M. Jayalakshmi and B. Sooryanarayana, Strong and Semi Strong Outer Mod Sum Graphs, Int. J. Math. Anal., 7 No. 2 (2013) 73-83.
[8] M. Jayalakshmi, B. Sooryanarayana and P. D. Rao, Outer Mod Sum Labelings of a Graph, Int. J. Inf. Sci. Comp. Math., 2 No. 2 (2010) 87-102.
[9] M. Jayalakshmi, B. Sooryanarayana and M. M. Padma, Outer Sum coloring of a graph, Universal Journal of Mathematics and Mathematical Sciences 7 No. 1 (2015) 33-49.
[10] B. Sooryanarayana, K. Manjula and M. Vishu Kumar, Outer Sum Labeling of a Graph, Int. J. Combin. graph theory and appl., 5 No. 2 (2020) 99-121.