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 A249997 #12 Jul 22 2022 01:27:30
%S A249997 1,2,15,40,221,702,3355,11780,52041,193402,817895,3138720,12953461,
%T A249997 50618102,206059635,813476860,3286192481,13047914802,52482224575,
%U A249997 209057202200,838843897101,3347530323502,13413657088715,53584020970740,214547906035321,857556157684202
%N A249997 Expansion of 1/((1-x)*(1+3*x)*(1-4*x)).
%H A249997 G. C. Greubel, <a href="/A249997/b249997.txt">Table of n, a(n) for n = 0..1000</a>
%H A249997 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,11,-12).
%F A249997 G.f.: 1/((1-x) * (1+3*x) * (1-4*x)).
%F A249997 a(n) = (-1)^n*3^(n+2)/28 + 4^(n+2)/21 -1/12. - _R. J. Mathar_, Jan 09 2015
%F A249997 E.g.f.: (1/84)*(27*exp(-3*x) - 7*exp(x) + 64*exp(4*x)). - _G. C. Greubel_, Jul 21 2022
%t A249997 LinearRecurrence[{2,11,-12}, {1,2,15}, 50] (* _G. C. Greubel_, Jul 21 2022 *)
%o A249997 (Magma) [((-1)^n*3^(n+3) +4^(n+3) -7)/84: n in [0..50]]; // _G. C. Greubel_, Jul 21 2022
%o A249997 (SageMath) [((-1)^n*3^(n+3) +4^(n+3) -7)/84 for n in (0..50)] # _G. C. Greubel_, Jul 21 2022
%Y A249997 Cf. A016208, A099621, A249998, A249999.
%K A249997 nonn,easy
%O A249997 0,2
%A A249997 _Alex Ratushnyak_, Dec 28 2014