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 A272794 #67 Jun 03 2018 02:03:36 %S A272794 0,0,1,1,2,5,13,27,74,198,508,1371,3809,10477,29116,82419,233748, %T A272794 666201,1914668,5528622,16019330,46642245,136326126,399652720, %U A272794 1175422931,3467251920,10258152021 %N A272794 The numbers of closed simply typable lambda terms of natural size n. %C A272794 Natural size measure lambda terms as follows: all symbols are assigned size 1, namely applications, abstractions, successor symbols in de Bruijn indices and 0 symbol in de Bruijn indices (i.e., a de Bruijn index n is assigned size n+1). %C A272794 Here we count the closed simply typable terms of natural size n. "Closed" means that there is no free index (no free bound variable). "Simply typable" means that lambda terms have a simple type. %C A272794 The numbers are computed as follows: all the closed terms are generated and then filtered using a type reconstruction algorithm. The values given above are the only known values of the sequence. %H A272794 Maciej Bendkowski, Katarzyna Grygiel, Pierre Lescanne, Marek Zaionc, <a href="https://arxiv.org/abs/1506.02367">A natural counting of Lambda terms</a>, arXiv:1506.02367 [cs.LO], 2015. %H A272794 Maciej Bendkowski, Katarzyna Grygiel, Pierre Lescanne, Marek Zaionc, <a href="http://www.sofsem.cz/sofsem16/files/presentations/Regular/Bendkowski.pdf">A Natural Counting of Lambda Terms</a>, SOFSEM 2016: 183-194 %H A272794 Maciej Bendkowski, K Grygiel, P Tarau, <a href="http://arxiv.org/abs/1612.07682">Random generation of closed simply-typed lambda-terms: a synergy between logic programming and Boltzmann samplers</a>, arXiv preprint arXiv:1612.07682, 2016 %Y A272794 Cf. A105633, A220471, A236393, A236405. %K A272794 nonn,more %O A272794 0,5 %A A272794 _Pierre Lescanne_, Jul 13 2016