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 A273396 #16 Nov 08 2016 07:36:24
%S A273396 0,1,3,9,39,201,1227,8305,61383,487761,4131819,37072361,350644047,
%T A273396 3482957945,36220558835,393329507169,4450157382383,52354044069009,
%U A273396 639307054297779,8090092395577625,105935581968131399,1433456549698679385,20018656224312123051
%N A273396 Indecomposable collections of multisets with a total of n objects having entries {1,2,...,k} for some k<=n or INVERTi transform of A255906.
%C A273396 A multiset partition of a multiset S is a set of nonempty multisets whose union is S. The total number of multisets of size n and whose entries have all the values in {1,2,...,k} for some k<=n is given by sequence A255906. A multiset partition is decomposable if there exists a value 1<=d<k such that every multiset A in the multiset partition either has max(A)<=d or min(A)>d. A multiset partition is called indecomposable otherwise.
%D A273396 P. A. MacMahon, Combinatory Analysis, vol 1, Cambridge, 1915.
%H A273396 Alois P. Heinz, <a href="/A273396/b273396.txt">Table of n, a(n) for n = 0..300</a>
%H A273396 R. Orellana, M. Zabrocki, <a href="http://arxiv.org/abs/1605.06672">Symmetric group characters as symmetric functions</a>, arXiv:1605.06672 [math.CO], 2016; or <a href="http://arxiv.org/abs/1510.00438">extended abstract</a>, arXiv:1510.00438 [math.CO], 2015.
%e A273396 a(3) = 9 because there are 16 multiset partitions, 9 of them are indecomposable ({{1},{1},{1}}, {{1},{1,1}}, {{1,1,1}}, {{1},{1,2}}, {{2},{1,2}}, {{1,1,2}}, {{1,2,2}}, {{2},{1,3}}, {{1,2,3}}) and 7 are decomposable ({{1},{1},{2}}, {{1},{2},{2}}, {{1},{2,2}}, {{2},{1,1}}, {{1},{2},{3}}, {{1},{2,3}}, {{3},{1,2}}).
%Y A273396 Cf. A074664, A003319.
%Y A273396 INVERTi transform of A255906.
%K A273396 nonn
%O A273396 0,3
%A A273396 _Mike Zabrocki_, May 21 2016