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 A152053 #24 Nov 07 2019 14:00:55
%S A152053 27,36,81,72,135,108,189,144,243,180,297,216,351,252,405,288,459,324,
%T A152053 513,360,567,396,621,432,675,468,729,504,783,540,837,576,891,612,945,
%U A152053 648,999,684,1053,720,1107
%N A152053 a(n) = A144433(3n+1) + A144433(3n+2) + A144433(3n+3).
%C A152053 All terms are multiples of 9.
%H A152053 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0, 2, 0, -1).
%F A152053 From _R. J. Mathar_, May 21 2009: (Start)
%F A152053 G.f.: 9*(3+4*x+3*x^2)/((x-1)^2*(1+x)^2).
%F A152053 a(n) = 45*(n+1)/2 + 9*(-1)^n*(n+1)/2. (End)
%F A152053 a(n) = 9*A106833(n+1). - _Jean-François Alcover_, Feb 02 2019, after _Paul Curtz_
%F A152053 a(n+4) = 2*a(n+2) - a(n). - _Jianing Song_, Feb 04 2019
%t A152053 Table[(9/2)(5 + (-1)^n)(n + 1), {n, 0, 40}] (* _Jean-François Alcover_, Feb 02 2019 *)
%t A152053 LinearRecurrence[{0,2,0,-1},{27,36,81,72},50] (* _Harvey P. Dale_, Nov 07 2019 *)
%o A152053 (PARI) a(n) = 45*(n+1)/2 + 9*(-1)^n*(n+1)/2 \\ _Jianing Song_, Feb 04 2019
%Y A152053 Cf. A106933, A144433.
%K A152053 nonn,easy
%O A152053 0,1
%A A152053 _Paul Curtz_, Nov 22 2008
%E A152053 Edited by _R. J. Mathar_, May 21 2009