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 A003840 #14 Jun 24 2025 11:03:29
%S A003840 2,129600,50759843097600,129182006871144805294080000,
%T A003840 2154683673871373733440812330742751559680000,
%U A003840 235766858527753399707968381023024646011879419539171573760000000
%N A003840 Order of (usually) simple Chevalley group D_n (9).
%D A003840 J. H. Conway, R. T. Curtis, S. P. Norton, R. A. Parker and R. A. Wilson, ATLAS of Finite Groups. Oxford Univ. Press, 1985 [for best online version see https://oeis.org/wiki/Welcome#Links_to_Other_Sites], p. xvi.
%D A003840 H. S. M. Coxeter and W. O. J. Moser, Generators and Relations for Discrete Groups, 4th ed., Springer-Verlag, NY, reprinted 1984, p. 131.
%H A003840 <a href="/index/Gre#groups">Index entries for sequences related to groups</a>.
%F A003840 a(n) = d(9,n) where d(q, n) is defined in A003837. - _Sean A. Irvine_, Sep 17 2015
%t A003840 d[q_, n_] := q^(n*(n-1)) * (q^n-1) * Product[q^(2*k) - 1, {k, 1, n-1}] / GCD[4, q^n-1]; Table[d[9, n], {n, 1, 8}] (* _Amiram Eldar_, Jun 24 2025 *)
%Y A003840 Cf. A003837, A003838, A003839.
%K A003840 nonn,easy
%O A003840 1,1
%A A003840 _N. J. A. Sloane_
%E A003840 a(6) from _Sean A. Irvine_, Sep 17 2015