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 A017558 #18 Aug 31 2018 02:53:30
%S A017558 9,225,729,1521,2601,3969,5625,7569,9801,12321,15129,18225,21609,
%T A017558 25281,29241,33489,38025,42849,47961,53361,59049,65025,71289,77841,
%U A017558 84681,91809,99225,106929,114921,123201
%N A017558 a(n) = (12*n + 3)^2.
%H A017558 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A017558 G.f.: 9*(1 + 22*x + 9*x^2)/(1-x)^3.
%F A017558 a(n) = 9*A016814(n).
%F A017558 a(n) = a(n-1) + 288*n - 72, n >= 1. - _Vincenzo Librandi_, Mar 20 2011
%t A017558 (12*Range[0,30]+3)^2 (* or *) LinearRecurrence[{3,-3,1},{9,225,729},30] (* _Harvey P. Dale_, Aug 04 2015 *)
%o A017558 (PARI) a(n)=(12*n+3)^2 \\ _Charles R Greathouse IV_, Jun 17 2017
%K A017558 nonn,easy
%O A017558 0,1
%A A017558 _N. J. A. Sloane_