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%I M3615 #28 Oct 29 2017 21:40:19
%S 1,1,4,26,255,3642,75606,2316169,106289210,7321773414,748425136289,
%T 111576624613588,23864968806932886,7225895692327786931,
%U 3064182503223082011556,1803904252801640389374494,1463405916763710662849541695,1625522872429294851288338156654
%N Number of topologies on n labeled points satisfying the T_4 axiom.
%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H Herman Jamke, <a href="/A006056/b006056.txt">Table of n, a(n) for n = 0..19</a>
%H M. Erné, <a href="http://dx.doi.org/10.1007/BF01173716">Struktur- und Anzahlformeln für Topologien auf Endlichen Mengen</a>, Manuscripta Math., 11 (1974), 221-259.
%H M. Erné, <a href="/A006056/a006056.pdf">Struktur- und Anzahlformeln für Topologien auf Endlichen Mengen</a>, Manuscripta Math., 11 (1974), 221-259. (Annotated scanned copy)
%F E.g.f.: A4(X) = exp(Z4(X)-1) where Z4(x) denotes the e.g.f. for A006058. - Herman Jamke, Mar 02 2008
%Y Sequences in the Erné (1974) paper: A000798, A001035, A006056, A006057, A001929, A001927, A006058, A006059, A000110.
%K nonn,nice
%O 0,3
%A _N. J. A. Sloane_
%E More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Mar 02 2008
%E More precise definition from _N. J. A. Sloane_, Jan 09 2014
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