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 A133669 #17 Jan 02 2024 08:56:20
%S A133669 1,7,-42,-385,1673,20538,-61439,-1067801,1942710,54264959,-40927831,
%T A133669 -2699910822,-694447103,131601183175,165629091222,-6282828884353,
%U A133669 -14398654354231,293459960979066,998994024336385,-13380544063637849,-62331251256120714
%N A133669 a(n) = a(n-1) - 49*a(n-2), a(0)=1, a(1)=7.
%H A133669 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (1, -49).
%F A133669 G.f.: (1+6*x)/(1-x+49*x^2) .
%F A133669 a(n) = Sum_{k=0..n} A133607(n,k)*7^k. - _Philippe Deléham_, Dec 30 2007
%t A133669 LinearRecurrence[{1,-49},{1,7},20] (* or *) CoefficientList[ Series[ (1+6x)/(1-x+49x^2),{x,0,20}],x] (* _Harvey P. Dale_, Sep 08 2018 *)
%Y A133669 Cf. A133607.
%K A133669 easy,sign
%O A133669 0,2
%A A133669 _Philippe Deléham_, Dec 28 2007
%E A133669 More terms from _Harvey P. Dale_, Sep 08 2018