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 A001217 #20 May 17 2025 06:09:19
%S A001217 1,2,4,6,8,12,24,48,120,192,384,720,1152,1920,3840,5040,23040,40320,
%T A001217 46080,51840,322560,362880,645120,2903040,3628800,5160960,10321920,
%U A001217 39916800,92897280,185794560,479001600,696729600,1857945600,3715891200
%N A001217 Sorted list of orders of Weyl groups of types A_n, B_n, D_n, E_n, F_4, G_2.
%H A001217 N. Bourbaki, <a href="http://dx.doi.org/10.1007/978-3-540-34491-9">Groupes et algèbres de Lie</a>, Chap. 4, 5, 6.
%F A001217 O(A_n) = (n+1)! = A000142(n+1), O(B_n) = O(C_n) = 2^n*n! = A000165(n), O(D_n) = 2^(n-1)*n! = A002866(n), O(E_n) = A003134(n), O(F_4) = 1152, O(G_2) = 12. Hence, {A001217} = {A000142} union {A000165} union {A002866} union {A003134} union {12, 1152}. - _Sean A. Irvine_, Jul 11 2019
%K A001217 nonn,easy,nice
%O A001217 1,2
%A A001217 _N. J. A. Sloane_