Abstract Based on some results for finite posets and the specialization order of a topology, as well as relationships between topologies and orderings, we calculate the total number of $T_0 $-topologies on a 5-element set, which is 4231. We also calculate the total number of different topologies on a 5-element set, which is 6942.
RONG Yu-yin, XU Luo-shan. Calculating of the total number of $T_0$-topologies on a 5-element set. Applied Mathematics A Journal of Chinese Universities, 2016, 31(4): 461-466.