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 A033566 #27 Jan 25 2025 18:46:04
%S A033566 -1,9,35,77,135,209,299,405,527,665,819,989,1175,1377,1595,1829,2079,
%T A033566 2345,2627,2925,3239,3569,3915,4277,4655,5049,5459,5885,6327,6785,
%U A033566 7259,7749,8255,8777,9315,9869,10439,11025,11627,12245,12879,13529,14195,14877,15575,16289,17019,17765
%N A033566 a(n) = (2*n+1) * (4*n-1).
%H A033566 G. C. Greubel, <a href="/A033566/b033566.txt">Table of n, a(n) for n = 0..1000</a>
%H A033566 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A033566 a(n) = A005408(n) * A004767(n-1). - _Michel Marcus_, Oct 03 2016
%F A033566 From _G. C. Greubel_, Oct 12 2019: (Start)
%F A033566 G.f.: (-1 + 12*x + 5*x^2)/(1-x)^3.
%F A033566 E.g.f.: (-1 + 10*x + 8*x^2)*exp(x). (End)
%F A033566 Sum_{n>=0} 1/a(n) = -2/3 +log(2)/6-Pi/12 = -0.81294152437.. - _R. J. Mathar_, May 07 2024
%p A033566 seq((2*n+1)*(4*n-1), n=0..50); # _G. C. Greubel_, Oct 12 2019
%t A033566 Table[(2*n+1)*(4*n-1), {n, 0, 50}] (* _G. C. Greubel_, Oct 12 2019 *)
%o A033566 (PARI) a(n) = (2*n+1) * (4*n-1); \\ _Michel Marcus_, Oct 03 2016
%o A033566 (Magma) [(2*n+1)*(4*n-1): n in [0..50]]; // _G. C. Greubel_, Oct 12 2019
%o A033566 (Sage) [(2*n+1)*(4*n-1) for n in range(50)] # _G. C. Greubel_, Oct 12 2019
%o A033566 (GAP) List([0..50], n-> (2*n+1)*(4*n-1)); # _G. C. Greubel_, Oct 12 2019
%Y A033566 Cf. A004767, A005408.
%K A033566 sign,easy
%O A033566 0,2
%A A033566 _N. J. A. Sloane_
%E A033566 Terms a(37) onward added by _G. C. Greubel_, Oct 12 2019