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 A327438 Irregular triangle read by rows with trailing zeros removed where T(n,k) is the number of unlabeled antichains of nonempty subsets of {1..n} with spanning edge-connectivity k. 2
 1, 1, 1, 3, 1, 6, 2, 1, 15, 7, 5, 2, 52, 53, 62, 31, 9, 1, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 COMMENTS An antichain is a set of sets, none of which is a subset of any other. The spanning edge-connectivity of a set-system is the minimum number of edges that must be removed (without removing incident vertices) to obtain a set-system that is disconnected or covers fewer vertices. LINKS EXAMPLE Triangle begins:    1    1  1    3  1    6  2  1   15  7  5  2   52 53 62 31  9  1  1 The antichains counted in row n = 4 are the following:   0             {1234}         {12}{134}{234}     {123}{124}{134}{234}   {1}           {12}{134}      {123}{124}{134}    {12}{13}{14}{23}{24}{34}   {12}          {123}{124}     {12}{13}{24}{34}   {123}         {12}{13}{14}   {12}{13}{14}{234}   {1}{2}        {12}{13}{24}   {12}{13}{14}{23}{24}   {1}{23}       {12}{13}{234}   {12}{13}      {12}{13}{14}{23}   {1}{234}   {12}{34}   {1}{2}{3}   {1}{2}{34}   {2}{13}{14}   {12}{13}{23}   {1}{2}{3}{4}   {4}{12}{13}{23} CROSSREFS Row sums are A306505. Column k = 0 is A327437. The labeled version is A327352. Cf. A014466, A052446, A327062, A327071, A327103, A327111, A327144, A327352, A327353. Sequence in context: A055151 A181187 A104573 * A010467 A335320 A182182 Adjacent sequences:  A327435 A327436 A327437 * A327439 A327440 A327441 KEYWORD nonn,tabf,more AUTHOR Gus Wiseman, Sep 11 2019 STATUS approved

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Last modified June 16 10:41 EDT 2021. Contains 345056 sequences. (Running on oeis4.)