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 A342501 #9 Mar 16 2021 08:30:49 %S A342501 1,0,2,0,6,6,0,38,84,24,0,390,1710,840,120,0,6062,49740,36840,8280, %T A342501 720,0,134526,2050566,2184000,646800,85680,5040,0,4172198,118645044, %U A342501 177549624,65313360,10735200,947520,40320 %N A342501 T(n,k) is the number of connected labeled posets with n elements and rank k: triangle read by rows. %C A342501 This is a variant of A342587 admitting only connected posets. %H A342501 <a href="/index/Pos#posets">Index entries for sequences related to posets</a> %e A342501 The table starts in row n=1 and shows ranks k>=0: %e A342501 1: 1 %e A342501 2: 0 2 %e A342501 3: 0 6 6 %e A342501 4: 0 38 84 24 %e A342501 5: 0 390 1710 840 120 %e A342501 6: 0 6062 49740 36840 8280 720 %e A342501 7: 0 134526 2050566 2184000 646800 85680 5040 %e A342501 8: 0 4172198 118645044 177549624 65313360 10735200 947520 40320 %Y A342501 Cf. A001927 (row sums), A000142 (diagonal), A002031/A002027 (rank 1), A342500 (unlabeled). %K A342501 nonn,tabl,hard %O A342501 1,3 %A A342501 _R. J. Mathar_, Mar 14 2021