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 A155607 #13 Dec 29 2018 18:08:57
%S A155607 1,11,89,755,6641,59291,532169,4785155,43053281,387440171,3486843449,
%T A155607 31381236755,282430067921,2541867422651,22876797237929,
%U A155607 205891146443555,1853020231898561,16677181828806731,150094635684419609
%N A155607 9^n+3^n-1.
%H A155607 <a href="/index/Rec">Index entries for linear recurrences with constant coefficients</a>, signature (13,-39,27).
%F A155607 G.f.: 1/(1-9*x)+1/(1-3*x)-1/(1-x). E.g.f.: e^(9*x)+e^(3*x)-e^x.
%F A155607 a(n)=12*a(n-1)-27*a(n-2)-16 with a(0)=1, a(1)=11 - _Vincenzo Librandi_, Jul 21 2010
%t A155607 LinearRecurrence[{13,-39,27},{1,11,89},20] (* _Harvey P. Dale_, Dec 29 2018 *)
%o A155607 (PARI) a(n)=9^n+3^n-1 \\ _Charles R Greathouse IV_, Jun 11 2015
%Y A155607 Cf. A155596, A155597, A155598, A155599, A155600, A155601, A155602, A155603, A155604, A155605, A155606.
%K A155607 nonn,easy
%O A155607 0,2
%A A155607 _Mohammad K. Azarian_, Jan 25 2009