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 A272764 #12 Dec 29 2024 10:56:34 %S A272764 3,10,20,36,63,120 %N A272764 Number of positive roots in reflection group E_n. %D A272764 J. E. Humphreys, Reflection Groups and Coxeter Groups, Cambridge, 1990. See Table 3.2, page 80. %H A272764 M. Golafshan, M. Rigo, and M. Whiteland, <a href="https://arxiv.org/abs/2412.18425">Computing the k-binomial complexity of generalized Thue-Morse words</a>, arXiv:2412.18425 [math.CO], 2024. See p. 29. %e A272764 Starting with the Coxeter-Dynkin diagram for E_8, one repeatedly chops off nodes from one end, getting the sequence E_8, E_7, E_6, D_5, A_4, A_2 X A_1, for which the numbers of positive roots are 120, 63, 36, 20, 10, 3 X 1=3. %Y A272764 Cf. A272696. %K A272764 nonn,fini,full %O A272764 3,1 %A A272764 _N. J. A. Sloane_, May 05 2016