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 A174809 #8 Sep 08 2022 08:45:51
%S A174809 1,4,68,3664,559296,292983296,677028302848,5742750182014976,
%T A174809 140199451387306704896,10334993471103615132237824,
%U A174809 3076052900280004094541239943168,3864163084421857020112275272686895104
%N A174809 A (100,-196) Somos 4 sequence.
%C A174809 Hankel transform of A174808.
%H A174809 G. C. Greubel, <a href="/A174809/b174809.txt">Table of n, a(n) for n = 0..60</a>
%F A174809 a(n) = (100*a(n-1)*a(n-3) - 196*a(n-2)^2)/a(n-4), n>3.
%t A174809 RecurrenceTable[{a[n] == (100*a[n-1]*a[n-3] -196*a[n-2]^2)/a[n-4], a[0] == 1, a[1] == 4, a[2] == 68, a[3] == 3664}, a, {n, 0, 20}] (* _G. C. Greubel_, Sep 18 2018 *)
%o A174809 (PARI) m=20; v=concat([1,4,68,3664], vector(m-4)); for(n=5, m, v[n] = ( 100*v[n-1]*v[n-3] - 196*v[n-2]^2)/v[n-4]); v \\ _G. C. Greubel_, Sep 18 2018
%o A174809 (Magma) I:=[1,4,68,3664]; [n le 4 select I[n] else (100*Self(n-1)*Self(n-3) - 196*Self(n-2)^2)/Self(n-4): n in [1..20]]; // _G. C. Greubel_, Sep 18 2018
%K A174809 easy,nonn
%O A174809 0,2
%A A174809 _Paul Barry_, Mar 29 2010