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 A196472 #35 Dec 27 2024 13:30:59
%S A196472 1,3,11,41,155,587,2225,8435,31979,121241,459659,1742699,6607073,
%T A196472 25049315,94969163,360055433,1365073787,5175387659,19621384337,
%U A196472 74390315987,282035100971,1069276250873,4053934055531,15369630919211,58270694924225,220920977530307,837575017363595
%N A196472 a(1)=1; a(n) = floor((3 + sqrt(21))*a(n-1)/2) for n > 1.
%C A196472 Contains only odd numbers.
%H A196472 Vincenzo Librandi, <a href="/A196472/b196472.txt">Table of n, a(n) for n = 1..150</a>
%H A196472 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,-3).
%F A196472 G.f.: -x*(-1+ x + x ^2) / ( (x-1)*(3*x^2 + 3*x - 1) ). - _R. J. Mathar_, Oct 04 2011
%F A196472 a(n) = (3 + 2*A108306(n))/15. - _R. J. Mathar_, Oct 04 2011
%t A196472 With[{c=(3+Sqrt[21])/2},NestList[Floor[c*#]&,1,30]] (* _Harvey P. Dale_, Apr 23 2014 *)
%o A196472 (Magma) I:=[1,3,11]; [n le 3 select I[n] else 4*Self(n-1)-3*Self(n-3): n in [1..30]]; // _Vincenzo Librandi_, Oct 05 2011
%Y A196472 Cf. A108306.
%K A196472 nonn,easy
%O A196472 1,2
%A A196472 _Philippe Deléham_, Oct 03 2011