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 A323786 #9 Jan 17 2023 12:36:52 %S A323786 1,0,2,3,19,39,200,615,2849,11174,52377,239269,1191090,6041975, %T A323786 32275288,177797719,1017833092,6014562272,36717301665,230947360981, %U A323786 1495562098099,9956230757240,68070158777759,477439197541792,3432259679880648,25267209686664449 %N A323786 Number of non-isomorphic weight-n multisets of multisets of non-singleton multisets. %C A323786 All sets and multisets must be finite, and only the outermost may be empty. %C A323786 The weight of an atom is 1, and the weight of a multiset is the sum of weights of its elements, counting multiplicity. %e A323786 Non-isomorphic representatives of the a(4) = 19 multiset partitions: %e A323786 {{1111}} {{1112}} {{1123}} {{1234}} %e A323786 {{11}{11}} {{1122}} {{11}{23}} {{12}{34}} %e A323786 {{11}}{{11}} {{11}{12}} {{12}{13}} {{12}}{{34}} %e A323786 {{11}{22}} {{11}}{{23}} %e A323786 {{12}{12}} {{12}}{{13}} %e A323786 {{11}}{{12}} %e A323786 {{11}}{{22}} %e A323786 {{12}}{{12}} %e A323786 Non-isomorphic representatives of the a(5) = 39 multiset partitions: %e A323786 {{11111}} {{11112}} {{11123}} {{11234}} {{12345}} %e A323786 {{11}{111}} {{11122}} {{11223}} {{11}{234}} {{12}{345}} %e A323786 {{11}}{{111}} {{11}{112}} {{11}{123}} {{12}{134}} {{12}}{{345}} %e A323786 {{11}{122}} {{11}{223}} {{23}{114}} %e A323786 {{12}{111}} {{12}{113}} {{11}}{{234}} %e A323786 {{12}{112}} {{12}{123}} {{12}}{{134}} %e A323786 {{22}{111}} {{13}{122}} {{23}}{{114}} %e A323786 {{11}}{{112}} {{23}{111}} %e A323786 {{11}}{{122}} {{11}}{{123}} %e A323786 {{12}}{{111}} {{11}}{{223}} %e A323786 {{12}}{{112}} {{12}}{{113}} %e A323786 {{22}}{{111}} {{12}}{{123}} %e A323786 {{13}}{{122}} %e A323786 {{23}}{{111}} %o A323786 (PARI) \\ See links in A339645 for combinatorial species functions. %o A323786 seq(n)={my(A=symGroupSeries(n)); NumUnlabeledObjsSeq(sCartProd(sExp(A), sExp(sExp(A-x*sv(1)))))} \\ _Andrew Howroyd_, Jan 17 2023 %Y A323786 Cf. A007716, A302545, A306186, A317791, A318564, A318566. %Y A323786 Cf. A323787, A323788, A323789, A323790, A323791, A323792, A323793, A323794. %K A323786 nonn %O A323786 0,3 %A A323786 _Gus Wiseman_, Jan 28 2019 %E A323786 Terms a(8) and beyond from _Andrew Howroyd_, Jan 17 2023