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 A089989 #11 Jul 07 2025 11:15:04
%S A089989 5,15000,29250000000,35703281250000000000,
%T A089989 27239372138671875000000000000000,
%U A089989 12988743471794208526611328125000000000000000000,3870947187719439049405530095100402832031250000000000000000000000,721020100095350865678782984846420731628313660621643066406250000000000000000000000000
%N A089989 a(n) = 5^(n^2+2n+1)*Product_{j=1..n} (25^j-1).
%C A089989 The order of the p-Clifford group for an odd prime p is a*p^(n^2+2n+1)*Product_{j=1..n} (p^(2*j)-1), where a = gcd(p+1,4).
%H A089989 G. Nebe, E. M. Rains and N. J. A. Sloane, <a href="http://neilsloane.com/doc/cliff2.html">Self-Dual Codes and Invariant Theory</a>, Springer, Berlin, 2006.
%F A089989 From _Amiram Eldar_, Jul 07 2025: (Start)
%F A089989 a(n) = A092300(n) / 2.
%F A089989 a(n) ~ c * 5^(2*n^2+3*n+1), where c = Product_{k>=1} (1 - 1/5^(2*k)) = 0.958400102563... . (End)
%t A089989 a[n_] := 5^(n^2+2*n+1) * Product[25^j - 1, {j, 1, n}]; Array[a, 10, 0] (* _Amiram Eldar_, Jul 07 2025 *)
%Y A089989 Cf. A001309, A003956.
%Y A089989 Cf. A092299 and A092301 (p=3), A092300 and A089989 (p=5), A090768 and A090769 (p=7), A090770 (p=2, although this is the wrong formula in that case).
%K A089989 nonn
%O A089989 0,1
%A A089989 _N. J. A. Sloane_, Feb 10 2004