This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A334252 #16 Apr 24 2020 01:02:34
%S A334252 1,2,5,44,2179,1362585,75953166947,14087646640499308474
%N A334252 Number of closure operators on a set of n elements which satisfy the T_0 separation axiom.
%C A334252 The T_0 axiom states that the closure of {x} and {y} are different for distinct x and y.
%H A334252 R. S. R. Myers, J. Adámek, S. Milius, and H. Urbat, <a href="https://doi.org/10.1016/j.tcs.2015.03.035">Coalgebraic constructions of canonical nondeterministic automata</a>, Theoretical Computer Science, 604 (2015), 81-101.
%H A334252 B. Venkateswarlu and U. M. Swamy, <a href="https://doi.org/10.1134/S1995080218090329">T_0-Closure Operators and Pre-Orders</a>, Lobachevskii Journal of Mathematics, 39 (2018), 1446-1452.
%F A334252 a(n) = Sum_{k=0..n} Stirling1(n,k) * A102896(k). - _Andrew Howroyd_, Apr 20 2020
%e A334252 The a(0) = 1 through a(2) = 5 set-systems of closed sets:
%e A334252 {{}} {{}} {{1,2},{1}}
%e A334252 {{1},{}} {{1,2},{2}}
%e A334252 {{1,2},{1},{}}
%e A334252 {{1,2},{2},{}}
%e A334252 {{1,2},{1},{2},{}}
%Y A334252 The number of all closure operators is given in A102896.
%Y A334252 For strict T0 closure operators, see A334253.
%Y A334252 For T1 closure operators, see A334254.
%Y A334252 Cf. A326943, A326944, A326945.
%K A334252 nonn,more
%O A334252 0,2
%A A334252 _Joshua Moerman_, Apr 20 2020
%E A334252 a(6)-a(7) from _Andrew Howroyd_, Apr 20 2020