Litta , E., and S. Narmadha. “Proper Colourings in R -Regular Inverse Sum Indeg Index Graphs”. Research and Applications Towards Mathematics and Computer Science Vol. 9 (February 5, 2024): 66–76. Accessed July 2, 2026. https://stm.bookpi.org/RATMCS-V9/article/view/13327.