On the number of topologies on a finite set

Abstract

We denote the number of distinct topologies which can be defined on a set X with n elements by T(n). Similarly, T0(n) denotes the number of distinct T0 topologies on the set X. In the present paper, we prove that for any prime p, T(pk ) ≡ k +1 (mod p), and that for each natural number n there exists a unique k such that T(p + n) ≡ k (mod p). We calculate k for n = 0, 1, 2, 3, 4. We give an alternative proof for a result of Z. I. Borevich to the effect that T0(p + n) ≡ T0(n + 1) (mod p).