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 A001513 #32 Feb 19 2023 03:33:24
%S A001513 5,77,221,437,725,1085,1517,2021,2597,3245,3965,4757,5621,6557,7565,
%T A001513 8645,9797,11021,12317,13685,15125,16637,18221,19877,21605,23405,
%U A001513 25277,27221,29237,31325,33485,35717,38021,40397,42845,45365,47957,50621,53357,56165,59045
%N A001513 a(n) = (6*n+1)*(6*n+5).
%H A001513 T. D. Noe, <a href="/A001513/b001513.txt">Table of n, a(n) for n = 0..1000</a>
%H A001513 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3,-3,1).
%F A001513 Sum_{k>=0} 1/a(k) = Pi/(8*sqrt(3)) = 0.22672492... - _Jaume Oliver Lafont_, May 30 2010
%F A001513 a(n) = 72*n + a(n-1) with a(0)=5. - _Vincenzo Librandi_, Nov 12 2010
%F A001513 G.f.: (-5 - 62*x - 5*x^2) / (x-1)^3. - _R. J. Mathar_, Jan 19 2013
%F A001513 From _Amiram Eldar_, Feb 19 2023: (Start)
%F A001513 a(n) = A016921(n)*A016969(n).
%F A001513 Sum_{n>=0} (-1)^n/a(n) = log(2+sqrt(3))/(4*sqrt(3)).
%F A001513 Product_{n>=0} (1 - 1/a(n)) = 2*cos(sqrt(5)*Pi/6).
%F A001513 Product_{n>=0} (1 + 1/a(n)) = 2*cos(sqrt(3)*Pi/6). (End)
%t A001513 a[n_] := (6*n + 1)*(6*n + 5); Array[a, 40, 0] (* _Amiram Eldar_, Feb 19 2023 *)
%o A001513 (PARI) a(n)=(6*n+1)*(6*n+5) \\ _Charles R Greathouse IV_, Jun 17 2017
%Y A001513 Cf. A016921, A016969.
%K A001513 nonn,easy
%O A001513 0,1
%A A001513 _N. J. A. Sloane_