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 A128941 #8 May 01 2024 13:43:19 %S A128941 4,28,138,629,2784,12134,52366,224404,956514,4060036,17175130, %T A128941 72454073,304941384,1280898302,5371301502,22491017756,94055344242, %U A128941 392888085098,1639534704630,6835739258996,28477594607346,118551827347574 %N A128941 Cardinality of the free modular lattice generated by two elements and a chain of length n. %C A128941 If you choose to adjoin a top and a bottom element to each resulting lattice, you must add 2 to these cardinalities: see A137400. %D A128941 G. Birkoff, Lattice Theory, American Mathematical Society, third edition (1967), pp. 63-64 [for the case n = 1]. %H A128941 M. P. Schützenberger, <a href="https://gallica.bnf.fr/ark:/12148/bpt6k31876/f926.item">Construction du treillis modulaire engendré par deux éléments et une chaine finie discrète</a>, Comptes Rendus de lAcad. Sci. Paris, vol. 235 (1952), pp. 926-928. %H A128941 K. Takeuchi, <a href="https://doi.org/10.2748/tmj/1178244623">On free modular lattices II</a>, Tohoku Mathematical Journal (2), vol. 11 (1959), pp. 1-12 [for the case n = 2]. %e A128941 When n = 0, the lattice consists of the two elements, their meet and their join, so a(0) = 4. %e A128941 When n = 1, we get the free modular lattice generated by three elements, so a(1) = 28. %Y A128941 Cf. A137400. %K A128941 nonn %O A128941 0,1 %A A128941 Lyle Ramshaw (lyle.ramshaw(AT)hp.com), Apr 08 2008 %E A128941 More terms from _Vladeta Jovovic_, Feb 05 2010