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 A189734 #30 Dec 31 2023 10:23:10
%S A189734 2,5,20,65,230,785,2720,9365,32330,111485,384620,1326665,4576430,
%T A189734 15786185,54454520,187839965,647952530,2235104885,7709972420,
%U A189734 26595469265,91740800630,316458947585,1091621898320,3765538534565,12989186560730,44806065794285
%N A189734 a(1)=2, a(2)=5, a(n)=2*a(n-1) + 5*a(n-2).
%H A189734 Vincenzo Librandi, <a href="/A189734/b189734.txt">Table of n, a(n) for n = 1..100</a>
%H A189734 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,5).
%F A189734 G.f.: x*(2+x)/(1-2*x-5*x^2). - _Bruno Berselli_, May 24 2011
%t A189734 LinearRecurrence[{2,5},{2,5},40]
%o A189734 (Maxima) a[1]:2$ a[2]:5$ a[n]:=2*a[n-1]+5*a[n-2]$ makelist(a[n], n, 1, 26); /* _Bruno Berselli_, May 24 2011 */
%Y A189734 Cf. A000045, A000079, A105476, A159612, A080040, A135522, A103435, A189732, A189735, A189736, A189737, A189738, A189739, A189741, A189742, A189743, A189744, A189745, A189746, A189747, A189748, A189749.
%K A189734 nonn
%O A189734 1,1
%A A189734 _Harvey P. Dale_, Apr 26 2011