Sun, Yongqi, Yang, Yuansheng, Lin, Xiaohui, and Zheng, Wenping. “The Value of the Ramsey Number R4(C4)”. Utilitas Mathematica 73 (June 9, 2007). Accessed April 18, 2026. https://utilitasmathematica.com/index.php/Index/article/view/481.