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 A038621 #25 Feb 04 2019 14:14:44
%S A038621 1,4,10,22,46,81,129,198,284,392,530,691,883,1114,1374,1674,2022,2405,
%T A038621 2837,3326,3856,4444,5098,5799,6567,7410,8306,9278,10334,11449,12649,
%U A038621 13942,15300,16752,18306,19931,21659,23498,25414,27442,29590,31821,34173,36654
%N A038621 Growth function of an infinite cubic graph (number of nodes at distance <=n from fixed node).
%C A038621 Partial sums of A038620.
%H A038621 Vincenzo Librandi, <a href="/A038621/b038621.txt">Table of n, a(n) for n = 0..1000</a>
%H A038621 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,2,-4,2,-1,2,-1).
%F A038621 a(0)=1, a(1)=4; for n>=2: if n == 0 (mod 3), a(n) = (4*n^3 + 6*n^2 + 15*n - 9)/9; if n == 1 (mod 3), a(n) = (4*n^3 + 6*n^2 + 18*n - 10)/9; if n == 2 (mod 3), a(n) = (4*n^3 + 6*n^2 + 15*n + 4)/9.
%F A038621 G.f.: (x+1)*(2*x^8-4*x^7+3*x^6-x^5+6*x^4+2*x^3+2*x^2+x+1) / ((x-1)^4*(x^2+x+1)^2). - _Colin Barker_, May 10 2013
%t A038621 CoefficientList[Series[(x + 1) (2 x^8 - 4 x^7 + 3 x^6 - x^5 + 6 x^4 + 2 x^3 + 2 x^2 + x + 1)/((x - 1)^4 (x^2 + x + 1)^2), {x, 0, 50}], x] (* _Vincenzo Librandi_, Oct 22 2013 *)
%t A038621 LinearRecurrence[{2,-1,2,-4,2,-1,2,-1},{1,4,10,22,46,81,129,198,284,392},50] (* _Harvey P. Dale_, Sep 03 2016 *)
%Y A038621 Cf. A038620, A290705.
%K A038621 nonn,easy
%O A038621 0,2
%A A038621 _Jan Kristian Haugland_
%E A038621 More terms from _Colin Barker_, May 10 2013