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 A174404 #19 Sep 08 2022 08:45:51
%S A174404 1,3,17,113,2801,84771,4561441,770238913,130385366497,63056004313443,
%T A174404 61225054070593841,67267054391287018481,273872013988285333139921,
%U A174404 1422475138861602537117455043,12376832685202654400796070741057
%N A174404 A (4,5)-Somos 4 sequence.
%C A174404 Hankel transform of A174403.
%H A174404 G. C. Greubel, <a href="/A174404/b174404.txt">Table of n, a(n) for n = 0..83</a>
%H A174404 Paul Barry, <a href="https://arxiv.org/abs/1910.00875">Generalized Catalan recurrences, Riordan arrays, elliptic curves, and orthogonal polynomials</a>, arXiv:1910.00875 [math.CO], 2019.
%F A174404 a(n) = (4*a(n-1)*a(n-3) + 5*a(n-2)^2)/a(n-4), n>=4.
%t A174404 RecurrenceTable[{a[0]==1,a[1]==3,a[2]==17,a[3]==113,a[n]== (4a[n-1] a[n-3]+ 5a[n-2]^2)/a[n-4]},a,{n,20}] (* _Harvey P. Dale_, May 20 2015 *)
%o A174404 (PARI) m=20; v=concat([1,3,17,113], vector(m-4)); for(n=5, m, v[n] = (4*v[n-1]*v[n-3] +5*v[n-2]^2)/v[n-4]); v \\ _G. C. Greubel_, Sep 22 2018
%o A174404 (Magma) I:=[1,3,17,113]; [n le 4 select I[n] else (4*Self(n-1)*Self(n-3) + 5*Self(n-2)^2)/Self(n-4): n in [1..20]]; // _G. C. Greubel_, Sep 22 2018
%K A174404 easy,nonn
%O A174404 0,2
%A A174404 _Paul Barry_, Mar 18 2010