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 A122996 #29 Dec 25 2021 03:30:33
%S A122996 1,7,56,399,3143,22694,176701,1288707,9947056,73093699,560499443,
%T A122996 4142090694,31606563401,234569007407,1783290614056,13277171976999,
%U A122996 100658412065743,751239838938694,5683502030160101,42494254138156107
%N A122996 Expansion of (1+6*x)/(1-x-49*x^2).
%H A122996 Nathaniel Johnston, <a href="/A122996/b122996.txt">Table of n, a(n) for n = 0..400</a>
%H A122996 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1,49)
%F A122996 a(n) = a(n-1) + 49*a(n-2). - _Philippe Deléham_, Mar 26 2009
%F A122996 a(n) = (1/2 + 13*sqrt(197)/394)*(1/2 + sqrt(197)/2)^n + (1/2 - 13*sqrt(197)/394)*(1/2 - sqrt(197)/2)^n. - _Antonio Alberto Olivares_, Jun 06 2011
%F A122996 a(n) = (7*i)^n*( ChebyshevU(n, -i/14) - (6*i/7)*ChebyshevU(n-1, -i/14) ). - _G. C. Greubel_, Dec 23 2021
%t A122996 M:= {{0, 1}, {1, 1/7}}; v[1] = {1,1}; v[n_]:= v[n]= M.v[n-1];
%t A122996 Table[v[n][[1]]*7^(n-1), {n,30}]
%t A122996 LinearRecurrence[{1,49}, {1,7}, 40] (* _G. C. Greubel_, Dec 23 2021 *)
%o A122996 (PARI) Vec((1+6*x)/(1-x-49*x^2) + O(x^30)) \\ _Michel Marcus_, Jan 28 2015
%o A122996 (Sage) [(7*i)^n*( chebyshev_U(n, -i/14) - (6*i/7)*chebyshev_U(n-1, -i/14) ) for n in (0..40)] # _G. C. Greubel_, Dec 23 2021
%o A122996 (Magma) [n le 2 select 7^(n-1) else Self(n-1) + 49*Self(n-2): n in [1..41]]; // _G. C. Greubel_, Dec 23 2021
%Y A122996 Cf. A122995.
%K A122996 nonn,easy
%O A122996 0,2
%A A122996 _Roger L. Bagula_, Sep 22 2006
%E A122996 Edited by the Associate Editors of the OEIS, Sep 09 2009