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 A166144 #30 Mar 17 2024 02:12:40
%S A166144 1,23,56,100,155,221,298,386,485,595,716,848,991,1145,1310,1486,1673,
%T A166144 1871,2080,2300,2531,2773,3026,3290,3565,3851,4148,4456,4775,5105,
%U A166144 5446,5798,6161,6535,6920,7316,7723,8141,8570,9010,9461,9923,10396,10880
%N A166144 a(n) = (11*n^2 + 11*n - 20)/2.
%H A166144 Vincenzo Librandi, <a href="/A166144/b166144.txt">Table of n, a(n) for n = 1..1000</a>
%H A166144 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A166144 a(n) = a(n-1) + 11*n, a(1)=1, with n>1.
%F A166144 From _Vincenzo Librandi_, Mar 15 2012: (Start)
%F A166144 G.f.: x*(1+20*x-10*x^2)/(1-x)^3.
%F A166144 a(n) = 3*a(n-1) -3*a(n-2) +a(n-3). (End)
%F A166144 E.g.f.: (1/2)*(-20 + 22*x + 11*x^2)*exp(x). - _G. C. Greubel_, Apr 26 2016
%F A166144 Sum_{n>=1} 1/a(n) = 1/10 + (2*Pi/sqrt(1001))*tan(sqrt(91/11)*Pi/2). - _Amiram Eldar_, Feb 20 2023
%t A166144 CoefficientList[Series[(1+20x-10x^2)/(1-x)^3,{x,0,50}],x] (* or *) LinearRecurrence[{3, -3, 1}, {1, 23, 56}, 50] (* _Vincenzo Librandi_, Mar 15 2012 *)
%t A166144 Table[(11 n^2 + 11 n - 20)/2, {n, 44}] (* _Michael De Vlieger_, Apr 27 2016 *)
%o A166144 (PARI) a(n)=11*binomial(n+1,2)-10 \\ _Charles R Greathouse IV_, Jan 11 2012
%o A166144 (Magma) I:=[1, 23, 56]; [n le 3 select I[n] else 3*Self(n-1)-3*Self(n-2)+1*Self(n-3): n in [1..40]]; // _Vincenzo Librandi_, Mar 15 2012
%K A166144 nonn,easy
%O A166144 1,2
%A A166144 _Vincenzo Librandi_, Oct 16 2009
%E A166144 New name from _Charles R Greathouse IV_, Jan 11 2012