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 A119827 #13 Jan 28 2021 16:43:46
%S A119827 0,0,0,1,4,16,60,212,728,2444,8064,26256,84576,270048,855936,2696080,
%T A119827 8446912,26341696,81812544,253181888,781005440,2402311616,7370247168,
%U A119827 22558917120,68901651456,210037106688,639127277568,1941624275200,5889576530944,17839902853120
%N A119827 Number of ternary words of length n with exactly one 000.
%C A119827 Except for the initial three zeros, convolution of A077835 with itself. Column 1 of A119825.
%H A119827 <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (4,0,-4,-12,-8,-4).
%F A119827 G.f.: z^3/(1-2z-2z^2-2z^3)^2.
%e A119827 a(4)=4 because we have 0001, 0002, 1000 and 2000.
%p A119827 h:=z^3/(1-2*z-2*z^2-2*z^3)^2: hser:=series(h,z=0,33): seq(coeff(hser,z,n), n=0..30);
%t A119827 LinearRecurrence[{4,0,-4,-12,-8,-4},{0,0,0,1,4,16},40] (* _Harvey P. Dale_, Jan 28 2021 *)
%Y A119827 Cf. A077835, A119825, A119826 (without 000), A231430 (one or more 000).
%K A119827 nonn,easy
%O A119827 0,5
%A A119827 _Emeric Deutsch_, May 26 2006